Functional oct data processing

ABSTRACT

A method of processing functional OCT image data, acquired by an OCT scanner scanning a retina that is being repeatedly stimulated by a light stimulus, to obtain a response of the retina to the light stimulus, comprising: receiving OCT image data generated by the OCT scanner repeatedly scanning the retina over a time period, and a sequence of stimulus indicators each indicative of a stimulation of the retina by the light stimulus in a respective time interval of a sequence of time intervals spanning the time period; calculating, for each stimulus indicator, a product of the stimulus indicator and a respective windowed portion of the sequence of B-scans comprising a B-scan based on a portion of the OCT image data generated while the retina was being stimulated in accordance with the stimulus indicator; and combining the calculated products to generate the indication of the response.

This application is a continuation of U.S. application Ser. No.16/930,465 filed Jul. 16, 2020, and claims the benefit of priority ofNetherlands Patent Application No. NL 2023578, filed Jul. 26, 2019, thecontents of each of which applications are incorporated by referenceherein in their entireties, as if set forth fully herein.

FIELD

Example aspects herein generally relate to the field of opticalcoherence tomography (OCT) data processing and, more particularly, tothe processing of functional OCT image data, which has been acquired byan OCT imaging device scanning a retina of a subject while the retina isbeing repeatedly stimulated by a light stimulus, to generate anindication of a response of the retina to the light stimulus.

BACKGROUND

Functional OCT provides an indication of how well a retina of an eyeresponds to light stimulation, and can provide a powerful tool forassessing the health of the eye. However, the amount of tomographic dataacquired in a typical functional OCT measurement, in which OCT data maybe acquired at a high data rate while the retina is being stimulated byhundreds or thousands of light flashes over a period of 20-30 seconds,for example, is usually very large (typically over 100 GB), and needs tobe correlated with information defining the timing of applied lightstimuli, making the processing of functional OCT data a complex taskthat can be very demanding on computer resources.

SUMMARY

To address at least some of the drawbacks of prior methods of processingfunctional OCT image data, there is provided, in accordance with a firstexample aspect herein, a computer-implemented method of processingfunctional OCT image data, which has been acquired by an OCT imagingdevice scanning a retina of a subject while the retina is beingrepeatedly stimulated by a light stimulus, to generate an indication ofa response of the retina to the light stimulus. The method comprisesreceiving, as the functional OCT image data: OCT image data that hasbeen generated by the OCT imaging device repeatedly scanning a scannedregion of the retina over a time period; and stimulus data defining asequence of stimulus indicators each being indicative of a stimulationof the retina by the light stimulus in a respective time interval of asequence of time intervals that spans the time period. The methodfurther comprises calculating a rolling window correlation between asequence of B-scans that is based on the OCT image data and stimulusindicators in the sequence of stimulus indicators by: calculating, foreach stimulus indicator, a product of the stimulus indicator and arespective windowed portion of the sequence of B-scans comprising aB-scan which is based on a portion of the OCT image data generated whilethe retina was being stimulated in accordance with the stimulusindicator; and combining the calculated products to generate theindication of the response of the retina to the light stimulus.

There is also provided, in accordance with a second example aspectherein, a computer-implemented method of processing functional OCT imagedata, which has been acquired by an OCT imaging device scanning a retinaof a subject while the retina is being repeatedly stimulated by a lightstimulus, to generate an indication of a response of the retina to thelight stimulus. The method comprises receiving, as the functional OCTimage data: OCT image data that has been generated by the OCT imagingdevice repeatedly scanning a scanned region of the retina over a timeperiod; and stimulus data defining a sequence of stimulus indicatorseach being indicative of a stimulation of the retina by the lightstimulus in a respective time interval of a sequence of time intervalsthat spans the time period. The method further comprises calculating arolling window correlation between a sequence of B-scans that is basedon the OCT image data and at least some of the stimulus indicators inthe sequence of stimulus indicators by calculating, for each stimulusindicator, a correlation between stimulus indicators in a windowcomprising the stimulus indicator and a predetermined number of adjacentstimulus indicators, and B-scans of the sequence of B-scans that arebased on a portion of the OCT image data generated while the retina wasbeing stimulated in accordance with the stimulus indicators in thewindow. The method further comprises generating the indication of theresponse of the retina to the light stimulus by combining the calculatedcorrelations.

There is also provided, in accordance with a third example aspectherein, a computer-implemented method of processing functional OCT imagedata, which has been acquired by an OCT imaging device scanning a retinaof a subject while the retina is being repeatedly stimulated by a lightstimulus, to generate image data defining an image that provides anindication of a response of the retina to the light stimulus. The methodcomprises receiving, as the functional OCT image data: OCT image datathat has been generated by the OCT imaging device repeatedly scanning ascanned region of the retina over a time period; and stimulus datadefining a sequence of stimulus indicators each being indicative of astimulation of the retina by the light stimulus in a respective timeinterval of a sequence of time intervals that spans the time period. Themethod further comprises calculating a rolling window correlationbetween a sequence of B-scans that is based on the OCT image data andstimulus indicators in the sequence of stimulus indicators. The methodfurther comprises using the calculated correlation to generate imagedata defining an image which indicates at least one of: the response ofthe scanned region of the retina to the light stimulus as a function oftime; one or more properties of a curve defining the response of thescanned region of the retina to the light stimulus as a function oftime; and a spatial variation, in the scanned region of the retina, ofone or more properties of the curve defining the response of the scannedregion of the retina to the light stimulus as a function of time, thespatial variation being overlaid on an en-face representation of atleast a portion the retina which includes the scanned region.

There is also provided, in accordance with a fourth example aspectherein, a computer program which, when executed by a processor, causesthe processor to perform a method according to at least one of the firstexample aspect, the second example aspect, or the third example aspectherein.

There is also provided, in accordance with a fifth example aspectherein, a non-transitory computer-readable storage medium storing thecomputer program according to the fourth example aspect herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments will now be explained in detail, by way ofnon-limiting example only, with reference to the accompanying figuresdescribed below. Like reference numerals appearing in different ones ofthe figures can denote identical or functionally similar elements,unless indicated otherwise.

FIG. 1 is a schematic illustration of an apparatus for processingfunctional OCT image data according to a first example embodimentherein.

FIG. 2 is a block diagram illustrating an example implementation of theapparatus of the first example embodiment in signal processing hardware.

FIG. 3 is a flow diagram illustrating a method of processing functionalOCT image data, which has been acquired by an OCT imaging devicescanning the subject's retina while the retina is being repeatedlystimulated by the light stimulus, to generate an indication of aresponse of the retina to the light stimulus in the first exampleembodiment herein.

FIG. 4 is a schematic illustration of functional OCT image data acquiredby a receiver module 110 in step S10 of FIG. 3 , and results ofprocessing the functional OCT image data in the first example embodimentherein.

FIG. 5 is a flow diagram illustrating a process by which athree-dimensional array of correlation values generated by a correlationcalculator mode 120-1 may further be processed to generate image data inthe first example embodiment herein.

FIG. 6(a) is a schematic illustration of a conversion of athree-dimensional array 700 of correlation values into a two-dimensionalarray 800 of correlation values by the correlation calculator module120-1 of the first example embodiment herein.

FIG. 6(b) is a schematic illustration of a first example process bywhich the correlation calculator module 120-1 of the first exampleembodiment herein may process the two-dimensional array 800 ofcorrelation values to generate a normalised two-dimensional array ofcorrelation values, 900-1.

FIG. 6(c) is a schematic illustration of a second example process bywhich the correlation calculator module 120-1 of the first exampleembodiment herein may process the two-dimensional array 800 ofcorrelation values to generate a normalised two-dimensional array ofcorrelation values, 900-2.

FIG. 7 is an example of an image defined by image data generated by animage data generator module 130 of the first example embodiment herein,which indicates a calculated response of the scanned region of theretina to an applied light stimulus as a function of time.

FIG. 8 is a schematic illustration of a division of each B-scan in asequence of B-scans into sets of adjacent A-scans and a subsequentconcatenating of resulting corresponding sets of A-scans to obtainrespective sections of a sequence of B-scans.

FIG. 9 is an example illustration of an image indicating respectivecorrelation strengths calculated for each of four different sections ofa scanned region of a retina, which are overlaid on a representation ofthe retina.

FIG. 10 is an example of a functional OCT report defined by image datawhich may be generated by an image data generation module of the firstexample embodiment herein.

FIG. 11 is a schematic illustration of an apparatus for processingfunctional OCT image data according to a second example embodimentherein.

FIG. 12 is a flow diagram illustrating a method of processing functionalOCT image data, which has been acquired by an OCT imaging devicescanning the subject's retina while the retina is being repeatedlystimulated by the light stimulus, to generate an indication of aresponse of the retina to the light stimulus in the second exampleembodiment herein.

FIG. 13 is a schematic illustration of a conversion of a sequence ofB-scans into a sequence of reduced B-scans by a B-scan processing module115 in the second example embodiment herein.

FIG. 14 is a schematic illustration of an apparatus for processingfunctional OCT image data according to a third example embodimentherein.

FIG. 15 is a flow diagram illustrating a method of processing functionalOCT image data, which has been acquired by an OCT imaging devicescanning the subject's retina while the retina is being repeatedlystimulated by the light stimulus, to generate an indication of aresponse of a layer of the retina to the light stimulus in the thirdexample embodiment herein.

FIG. 16 is a schematic illustration of a segmentation of B-scans by aB-scan processing module 117 into B-scan layers in the third exampleembodiment herein.

FIG. 17 is a schematic illustration of an apparatus for processingfunctional OCT image data according to a fourth example embodimentherein.

FIG. 18 is a flow diagram illustrating a method of processing functionalOCT image data, which has been acquired by an OCT imaging devicescanning the subject's retina while the retina is being repeatedlystimulated by the light stimulus, to generate an indication of aresponse of a layer of the retina to the light stimulus in the fourthexample embodiment herein.

FIG. 19 is a schematic illustration of an apparatus for processingfunctional OCT image data according to a fifth example embodimentherein.

FIG. 20 is a flow diagram illustrating a method of processing functionalOCT image data, which has been acquired by an OCT imaging devicescanning the subject's retina while the retina is being repeatedlystimulated by the light stimulus, to generate an indication of aresponse of the retina to the light stimulus in the fifth exampleembodiment herein.

FIG. 21 is a schematic illustration of functional OCT image dataacquired by the receiver module 110 in step S10 of FIG. 3 , and resultsof processing the functional OCT image data in the fifth exampleembodiment herein.

FIG. 22 is a flow diagram illustrating a process by which thethree-dimensional array of correlation values generated by a responsegenerator module 125-5 may be processed to generate image data in thefifth example embodiment herein.

FIG. 23(a) is a schematic illustration of a conversion of athree-dimensional array 700′ of combined correlation values into atwo-dimensional array 800′ of combined correlation values by theresponse generator module 125-5 of the fifth example embodiment herein.

FIG. 23(b) is a schematic illustration of a first example process bywhich the response generator module 125-5 of the fifth exampleembodiment herein may process the two-dimensional array 800′ of combinedcorrelation values to generate a normalised two-dimensional array ofcombined correlation values, 900′-1.

FIG. 23(c) is a schematic illustration of a second example process bywhich the response generator module 125-5 of the fifth exampleembodiment herein may process the two-dimensional array 800′ of combinedcorrelation values to generate a normalised two-dimensional array ofcombined correlation values, 900′-2.

FIG. 24 is a schematic illustration of an apparatus for processingfunctional OCT image data according to a sixth example embodimentherein.

FIG. 25 is a flow diagram illustrating a method of processing functionalOCT image data, which has been acquired by an OCT imaging devicescanning the subject's retina while the retina is being repeatedlystimulated by the light stimulus, to generate an indication of aresponse of the retina to the light stimulus in the sixth exampleembodiment herein.

FIG. 26 is a schematic illustration of an apparatus for processingfunctional OCT image data according to a seventh example embodimentherein.

FIG. 27 is a flow diagram illustrating a method of processing functionalOCT image data, which has been acquired by an OCT imaging devicescanning the subject's retina while the retina is being repeatedlystimulated by the light stimulus, to generate an indication of aresponse of a layer of the retina to the light stimulus in the seventhexample embodiment herein.

FIG. 28 is a schematic illustration of an apparatus for processingfunctional OCT image data according to an eighth example embodimentherein.

FIG. 29 is a flow diagram illustrating a method of processing functionalOCT image data, which has been acquired by an OCT imaging devicescanning the subject's retina while the retina is being repeatedlystimulated by the light stimulus, to generate an indication of aresponse of a layer of the retina to the light stimulus in the eighthexample embodiment herein.

DETAILED DESCRIPTION OF EMBODIMENTS

There is described herein, by way of example embodiments, an apparatusfor processing functional OCT image data, which has been acquired by anOCT imaging device scanning a retina of a subject while the retina isbeing repeatedly stimulated by a light stimulus, to generate image datadefining an image that provides an indication of a response of theretina to the light stimulus. The apparatus comprises a receiver moduleconfigured to receive, as the functional OCT image data: OCT image datathat has been generated by the OCT imaging device repeatedly scanning ascanned region of the retina over a time period; and stimulus datadefining a sequence of stimulus indicators each being indicative of astimulation of the retina by the light stimulus in a respective timeinterval of a sequence of time intervals that spans the time period. Theapparatus further comprises a correlation calculator module configuredto calculate a rolling window correlation between a sequence of B-scansthat is based on the OCT image data and stimulus indicators in thesequence of stimulus indicators. The rolling window correlation may becalculated in a number of different ways. For example, the correlationcalculator module may calculate the rolling window correlation betweenthe sequence of B-scans and the stimulus indicators in the sequence ofstimulus indicators by calculating, for each of a plurality of windowedportions of the sequence of B-scans, a respective product of a stimulusindicator in accordance which the retina was stimulated while OCT imagedata, on which at least one of the B-scans in the windowed portion ofthe sequence of B-scans is based, was being generated by the OCT imagingdevice, and at least a portion of each B-scan in the windowed portion ofthe sequence of B-scans. The correlation calculator module mayalternatively calculate the rolling window correlation between thesequence of B-scans and the stimulus indicators in the sequence ofstimulus indicators by calculating, for each stimulus indicator, acorrelation between stimulus indicators in a window comprising thestimulus indicator and a predetermined number of adjacent stimulusindicators, and B-scans of the sequence of B-scans that are based on aportion of the OCT image data generated while the retina was beingstimulated in accordance with the stimulus indicators in the window.Some example methods of calculating the rolling window correlation thatmay be employed by the correlation calculator module are set out in thefollowing description of example embodiments.

The apparatus set out above further comprises an image data generatormodule configured to use the calculated rolling window correlation togenerate image data defining an image which indicates at least one of:the response of the scanned region of the retina to the light stimulusas a function of time; one or more properties of a curve defining theresponse of the scanned region R of the retina to the light stimulus asa function of time; and a spatial variation, in the scanned region ofthe retina, of one or more properties of the curve defining the responseof the scanned region of the retina to the light stimulus as a functionof time, the spatial variation being overlaid on an en-facerepresentation of at least a portion the retina which includes thescanned region.

There is also described in the following, by way of example embodiments,a computer-implemented method of processing functional OCT image data,which has been acquired by an OCT imaging device scanning a retina of asubject while the retina is being repeatedly stimulated by a lightstimulus, to generate image data defining an image that provides anindication of a response of the retina to the light stimulus. The methodcomprises receiving, as the functional OCT image data: OCT image datathat has been generated by the OCT imaging device repeatedly scanning ascanned region of the retina over a time period; and stimulus datadefining a sequence S of stimulus indicators each being indicative of astimulation of the retina by the light stimulus in a respective timeinterval of a sequence of time intervals that spans the time period. Themethod further comprises calculating a rolling window correlationbetween a sequence of B-scans that is based on the OCT image data andstimulus indicators in the sequence S of stimulus indicators, asmentioned above. The method further comprises using the calculatedrolling window correlation to generate image data defining an imagewhich indicates at least one of: the response of the scanned region ofthe retina to the light stimulus as a function of time; one or moreproperties of a curve defining the response of the scanned region of theretina to the light stimulus as a function of time; and a spatialvariation, in the scanned region of the retina, of one or moreproperties of the curve defining the response of the scanned region ofthe retina to the light stimulus as a function of time, the spatialvariation being overlaid on an en-face representation of at least aportion of the retina which includes the scanned region.

Example embodiments herein will now be described in more detail withreference to the accompanying drawings.

Embodiment 1

FIG. 1 is a schematic illustration of an apparatus 100-1 according to afirst example embodiment, which is configured to process functionalOptical Coherence Tomography (OCT) image data to generate an indicationof how well a retina 10 of a subject's eye 20 responds to a flickeringlight stimulus. The functional OCT data processed by the apparatus 100-1is acquired by an OCT imaging device 200, specifically by the OCTimaging device 200 employing an ophthalmic scanner (not shown) to scanan OCT sample beam generated by an OCT measurement module 210 across aregion R of the subject's retina 10 while the retina 10 is beingrepeatedly stimulated by a light stimulus generated by a light stimulusgenerator 220 of the OCT imaging device 200.

The light stimulus may, as in the present example embodiment, comprise afull-field light stimulus (or flash), which provides substantiallyuniform illumination (at wavelengths in the visible spectrum betweenabout 380 and 740 nm in the present example, although other wavelengthscould alternatively or additionally be used) that fills the whole visualfield of the subject. The light stimulus generator 220 may, for example,comprise a light-emitting diode (LED) or other optical emitter forgenerating the light stimuli. The flashes that the light stimulusgenerator 220 emits may, as in the present example embodiment, give riseto a random (or pseudo-random) stimulation of the retina over time. Inother words, the light stimulus generator 220 may emit light flashesthat are randomly or pseudo-randomly distributed in time, so that thesubject cannot (subconsciously) learn to anticipate upcoming flashes,thereby allowing a more accurate functional response to the subject'sretina 10 to light stimulation to be measured.

It should be noted, however, that the light stimulus need not be afull-field stimulus, and may alternatively stimulate only a portion ofthe retina, which may be illuminated in accordance with a structuralscan pattern (e.g. an annulus, a hypotrochoid, or Lissajous figure, forexample) by the ophthalmic scanner (not shown) of the OCT imaging device200.

As illustrated in FIG. 1 , the apparatus 100-1 of the present exampleembodiment comprises a receiver module 110, a correlation calculatormodule 120-1 and, optionally, an image data generator module 130, whichare communicatively coupled (e.g. via a bus 140) so as to be capable ofexchanging data with one another and with the OCT imaging device 200.

FIG. 2 is a schematic illustration of a programmable signal processinghardware 300, which may be configured to process functional OCT datausing the techniques described herein and, in particular, function asthe receiver module 110, the correlation calculator module 120-1 and the(optional) image data generator module 130 of the first exampleembodiment. The programmable signal processing hardware 300 comprises acommunication interface (I/F) 310 for receiving the functional OCT datafrom the OCT imaging device 200, and outputting image data describedherein below, which defines an image indicating the response of theretina to the light stimulus. The signal processing apparatus 300further comprises a processor (e.g. a Central Processing Unit, CPU, orGraphics Processing Unit, GPU) 320, a working memory 330 (e.g. a randomaccess memory) and an instruction store 340 storing a computer program345 comprising the computer-readable instructions which, when executedby the processor 320, cause the processor 320 to perform variousfunctions including those of the receiver module 120-1, the correlationcalculator module 120-1 and/or the image data generator module 130described herein. The working memory 330 stores information used by theprocessor 320 during execution of the computer program 345, includingintermediate processing results such as the calculated products ofstimulus indicators and respective windowed portions of the sequence ofB-scans, for example. The instruction store 340 may comprise a ROM (e.g.in the form of an electrically-erasable programmable read-only memory(EEPROM) or flash memory) which is pre-loaded with the computer-readableinstructions. Alternatively, the instruction store 340 may comprise aRAM or similar type of memory, and the computer-readable instructions ofthe computer program 345 can be input thereto from a computer programproduct, such as a non-transitory, computer-readable storage medium 350in the form of a CD-ROM, DVD-ROM, etc. or a computer-readable signal 360carrying the computer-readable instructions. In any case, the computerprogram 345, when executed by the processor 320, causes the processor320 to execute a method of processing functional OCT data as describedherein. It should be noted, however, that the receiver module 110, thecorrelation calculator module 120-1 and/or the image data generatormodule 130 may alternatively be implemented in non-programmablehardware, such as an application-specific integrated circuit (ASIC).

In the present example embodiment, a combination 370 of the hardwarecomponents shown in FIG. 2 , comprising the processor 320, the workingmemory 330 and the instruction store 340, is configured to performfunctions of the receiver module 110, the correlation calculator module120-1 and the image data generator module 130 that are described below.

FIG. 3 is a flow diagram illustrating a method performed by theprocessor 320, by which the processor 320 processes functional OCT data,which has been acquired by the OCT imaging device 200 scanning thesubject's retina 10 while the retina 10 is being repeatedly stimulatedby the light stimulus, to generate an indication of a response of theretina 10 to the light stimulus.

In step S10 of FIG. 3 , the receiver module 110 receives from the OCTimaging device 200, as the functional OCT image data: (i) OCT image datathat has been generated by the OCT imaging device 200 repeatedlyscanning a scanned region R of the retina 10 over a time period T; and(ii) stimulus data defining a sequence of s stimulus indicators, eachstimulus indicator being indicative of a stimulation of the retina 10 bythe light stimulus in a respective time interval, T/s, of a sequence oftime intervals that spans the time period T.

The received OCT image data may, as in the present example embodiment,comprise a sequence of b B-scans, which has been generated by the OCTimaging device 200 repeatedly scanning the scanned region R of theretina 10 over the time period T. FIG. 4 illustrates functional OCTimage data acquired by the receiver module 110 in step S10 of FIG. 3 .As illustrated in FIG. 4 , each B-scan 400 in the sequence of B-scanscan be represented as a 2D image made up of a A-scans (vertical lines).Each A-scan comprises a one-dimensional array of d pixels, where thepixel value of each pixel represents a corresponding OCT measurementresult, and the location of each pixel in the one-dimensional array isindicative of the OCT measurement location in the axial direction of theOCT imaging device 200, at which location the corresponding pixel valuewas measured. The OCT image data can thus be represented as athree-dimensional pixel array 500, which is a×b×d pixels in size.

It should be noted that each A-scan in the B-scan 400 may be an averageof a number of adjacent A-scans that have been acquired by the OCTimaging device 200. In other words, the OCT imaging device 200 mayacquire A-scans having lateral spacing (e.g. along the surface of theretina) which is smaller than the optical resolution of the OCT imagingdevice 200, and average sets of adjacent A-scans to generate a set ofaveraged A-scans which make up a B-scans displaying improvedsignal-to-noise.

The OCT imaging device 200 generates the OCT image data by scanning alaser beam across the scanned region R of the retina 10 in accordancewith a predetermined scan pattern, acquiring the A-scans that are tomake up each B-scan 400 as the scan location moves over the scannedregion R. The shape of the scan pattern on the retina 10 is not limited,and is usually determined by a mechanism in the OCT imaging device 200that can steer the laser beam generated by the OCT measurement module210. In the present example embodiment, galvanometer (“galvo”) motors,whose rotational position values are recorded, are used to guide thelaser beam during the acquisition of the OCT data. These positions canbe correlated to locations on the retina 10 in various ways, which willbe familiar to those versed in the art. The scan pattern may, forexample, trace out a line, a curve, or a circle on the surface of theretina 10, although a lemniscate scan pattern is employed in the presentexample embodiment. The A-scans acquired during each full period of thescan pattern form one B-scan. In the present example embodiment, all ofthe b B-scans are recorded in the time period T, such that the time perB-scan is T/b, and the scan pattern frequency is b/T.

During the time period T, while the OCT image data is being generated bythe OCT imaging device 200, a stimulus is shown to the subject, whichcan be a full-field stimulus (substantially the same brightness valueover the whole visual field), as in the present example embodiment, or aspatial pattern, where the visual field is divided into e.g. squares,hexagons or more complicated shapes. In the case of a full-fieldstimulus, at any point in time, the brightness can be denoted, forexample, as either “1” (full brightness) or as “−1” (darkness, with nostimulus having been applied). The time period Tis divided into asequence of s time intervals (corresponding to the “stimulus positions”referred to herein), each of size Vs and, for each time interval, thereis an associated stimulus indicator (s₁, s₂, s₃ . . . ) which isindicative of a stimulation of the retina 10 by the light stimulus inthe respective time interval T/s. Thus, each stimulus indicator in thesequence of stimulus indicators may take a value of either 1 or −1(although the presence or absence of the stimulus may more generally bedenoted by n and −n, where n is an integer). The concatenation of thestimulus indicator values that are indicative of the stimulation of theretina 10 during OCT image data generation is referred to herein as asequence S of stimulus indicators. One choice for S is an m-sequence,which is a pseudo-random array. In alternative embodiments, in whichthere is a spatial pattern to the stimulus, each individual field caneither display a completely different m-sequence, or a version of onem-sequence that is (circularly) delayed by a specific time, or aninversion of one m-sequence (i.e. when one field shows a 1, anothershows a −1 and vice versa). As noted above, the receiver module 110 isconfigured to receive stimulus data defining the sequence S of stimulusindicators s₁, s₂, s₃, etc. The receiver module 110 may, for example,receive information defining the sequence S of stimulus indicatorsitself, or alternatively information that allows the sequence S ofstimulus indicators to be constructed by the apparatus 100-1.

It should be noted that, although each stimulus indicator in thesequence S of stimulus indicators is indicative of whether or not theretina 10 was stimulated by the light stimulus in the corresponding timeinterval of duration T/s, the stimulus indicator is not so limited, andmay, in other example embodiments, be indicative of a change instimulation of the retina 10 by the light stimulus that occurs in arespective time interval of the sequence S of time intervals that spansthe time period T. For example, in the following description ofcorrelation calculations, each windowed portion of the sequence ofB-scans may be multiplied by −1 if the stimulus changes from +1 to ˜1 inthe associated time interval T/s, by +1 if the stimulus changes from −1to +1 in the associated time interval T/s, and by zero if the stimulusdoes not change in the time interval.

After at least some of the functional OCT data have been received by thereceiver module 110, the correlation calculator 120-1 begins tocalculate a rolling window correlation between a sequence of B-scansthat is based on the OCT image data and at least some of the stimulusindicators in the sequence S of stimulus indicators.

More particularly, the correlation calculator module 120-1 calculatesthe rolling window correlation firstly by calculating, in step S20-1 ofFIG. 3 , for each of the stimulus indicators s₁, s₂, s₃, etc., a productof the stimulus indicator and a respective windowed portion of thesequence of B-scans 500 comprising a predetermined number, b_(lag), ofB-scans, beginning with (or otherwise including) a B-scan which is basedon a portion of the OCT image data generated while the retina 10 wasbeing stimulated in accordance with the stimulus indicator. Thecorrelation calculator module 120-1 thus generates in step S20-1 of FIG.3 a plurality of calculated products. It should be noted that theintervals T/b and T/s are not necessarily equal, and that there are b/sB-scans per stimulus position/indicator, or s/b stimuli per B-scan. Byway of an example, b/s=2 in the present example embodiment, so that twoB-scans are generated by the OCT imaging device 200 while the retina isbeing stimulated, or is not being stimulated (as the case may be), inaccordance with each stimulus indicator value. Thus, the correlationcalculator module 120-1 calculates a product of the value of the firststimulus indicator s₁, which is −1 in the example of FIG. 4 , and eachof the data elements of a first portion (or block) 600-1 of thethree-dimensional array of pixels 500, which portion 600-1 isa×b_(lag)×d pixels in size and includes two B-scans that were generatedby the OCT imaging device 200 while the retina was not being stimulated(in accordance with the stimulus indicator value “−1” applicable for thetime interval from time t=0 to t=T/s) and six subsequent B-scans, asb_(lag)=8 in the example of FIG. 4 (although other values for b_(lag)could alternatively be used). The value of b_(lag) is preferably set tocorrespond to the number of B-scans generated by the OCT imaging device200 in a period of no more than about 1 second, as the use of greatervalues of b_(lag) may make little or no improvement to the calculatedretinal response, whilst making the calculation more demanding ofcomputational resources. In other words, the correlation calculatormodule 120-1 multiplies each matrix element of a matrix, which is formedby the portion 600-1 of the three-dimensional array 500 of pixels thatis a×b_(lag)×d pixels in size, by the value (“−1”) of the first stimulusindicator, s₁, in the sequence S of indicator values defined by thereceived stimulus data. Then, for the second stimulus indicator, s₂, inthe sequence S of stimulus indicators (having the value “+1”), each dataelement of the data elements of a second portion (or block) 600-2 of thethree-dimensional pixel array 500, which second portion 600-2 is alsoa×b_(lag)×d pixels in size but begins with the two B-scans that weregenerated by the OCT imaging device 200 while the retina was beingstimulated (in accordance with the second stimulus indicator value “+1”applicable for the time interval from time t=T/s to t=2T/s) and alsoincludes six adjacent, subsequent B-scans, by the corresponding stimulusindicator value “+1”. This multiplication process is repeated for theremaining stimulus indicators in the sequence S of stimulus indicators,with the correlation calculator module 120-1 moving the rolling windowforward in time by one time interval T/s in each step of the process, sothat it slides past the second stimulus indicator, s₁, in the sequence Sof stimulus indicators and covers the stimulus indicator immediatelyadjacent the right-hand boundary of the rolling window as it waspreviously positioned, and the product of the stimulus indicator andwindowed portion of the sequence of B-scans 500 is calculated onceagain, using the newly-windowed portion of the sequence S of stimulusindicators and the corresponding B-scans in the sequence of B-scans 500to generate another block of eight weighted B-scans. This procedure ofsliding the rolling window forward in time and calculating the productto obtain a block of weighted B-scans for each rolling window positionis repeated until the rolling window reaches the end of the sequence Sof stimulus indicators, thereby generating a plurality of data blocksthat are each a×b_(lag)×d pixels in size, as illustrated in FIG. 4 .

In step S30 of FIG. 3 , the correlation calculator module 120-1 combinesthe calculated products, thus generating an indication of the responseof the retina 10 to the light stimulus. In the present exampleembodiment, the correlation calculator module 120-1 combines thecalculated products by performing a matrix addition of the plurality ofdata blocks 600-1, 600-2 . . . etc. generated in step S20-1, which areeach a×b_(lag)×d pixels in size, to generate a response block (alsoreferred to herein as a “response volume”) 700, which is athree-dimensional array of correlation values that is likewisea×b_(lag)×d array elements in size. The correlation values in theresponse block 700 may each be divided by s, to obtain a normalisedresponse.

As an alternative to the correlation calculation described above (sum ofstimulus values multiplied with OCT blocks), it is also possible to usea more advanced normalisation cross-correlation that takes into accountmean and standard deviation of the intensities in the sequence ofB-scans 500 and mean and standard deviation of stimulus values in thesequence of stimulus indicators S. Such normalisation cross-correlationmay be calculated using the “norm×corr2” function in Matlab™, forexample.

The three-dimensional array 700 of correlation values may further beprocessed by the correlation calculator module 120-1, and the results ofthose further processing operations may be used by the image datagenerator module 130 to generate image data defining an image whichindicates the response of the retina to the light stimulus for displayto a user of the apparatus 100-1, so that an assessment of how well theretina responds to stimulation can be made. These optional furtherprocessing operations will now be described with reference to the flowdiagram in FIG. 5 .

The response volume 700 may be reduced to a two-dimensional responseimage for easier visualisation by taking the average in the depth (d)direction, i.e. one value per A-scan per lag time point. Thus, in(optional) step S40 of FIG. 5 , the correlation calculator module 120-1converts the three-dimensional array 700 of correlation values, which isa×b_(lag)×d pixels in size, into a two-dimensional array 800 ofcorrelation values, which is a×b_(lag) pixels in size (as illustrated inFIG. 6(a)), by replacing each one-dimensional array of correlationvalues in the three-dimensional array 700, which one-dimensional arrayhas been calculated using A-scans that are identically located inrespective B-scans of the sequence 500 of B-scans, with a single valuethat is an average of the correlation values in the one-dimensionalarray. The two-dimensional array 800 of correlation values indicates theresponse of the retina 10 to the light stimulus as a function oflocation along the scanned region R of the retina 10 (i.e. as a functionof position along the line defining the scan pattern) and time.

The image data generator module 130 may use the two-dimensional array800 of correlation values to generate image data defining an image whichindicates the response of the retina to the light stimulus as a functionof location in the scanned region of the retina and time, where thevalues of a and b_(lag) determine the extent of the spatial and temporalvariations of the response. However, it may be preferable to pre-processthe two-dimensional array 800 of correlation values generated in stepS40 prior to image data generation (or prior to the alternative furtherprocessing operation described below), in order to accentuate thetime-dependent variability of the signal, i.e. the variation of theretinal response to light stimulation over time. Such pre-processing maybe desirable in cases where the response variability in the A-scandirection is greater than in the time lag direction.

The correlation calculator module 120-1 may pre-process thetwo-dimensional array 800 of correlation values, which comprises asequence of b_(lag) one-dimensional arrays (A₁, A₂, . . . A_(b) _(lag)), each indicating the response of the retina 10 to the light stimulusas a function of location in the scanned region R of the retina 10, bygenerating a normalised two-dimensional array of correlation values. Thecorrelation calculator module 120-1 may, as illustrated in FIG. 6(b),generate a normalised two-dimensional array, 900-1, of correlationvalues by subtracting the first one-dimensional array, A₁, in thesequence of one-dimensional arrays from each remaining one-dimensionalarray (A₂, A₃, . . . , A_(b) _(lag) ) in the sequence of one-dimensionalarrays. Alternatively, the correlation calculator module 120-1 maygenerate a normalised two-dimensional array of correlation values,900-2, by calculating an array of averaged correlation values,

${\overset{\_}{A} = {\frac{1}{b_{lag}}{\sum\limits_{n = 1}^{b_{lag}}A_{n}}}},$such that each averaged correlation value in the array of averagedcorrelation values is an average (mean) of the correlation values thatare correspondingly located in the sequence of one-dimensional arrays,and subtracting the calculated array of averaged correlation values, Ā,from each of the one-dimensional arrays (A₁, A₂, A₃, . . . , A_(b)_(lag) ) in the sequence of one-dimensional arrays (in other words,performing a vector subtraction of the calculated array of averagedcorrelation values from each of the one-dimensional arrays), asillustrated in FIG. 6(c). In both of these alternative ways ofcalculating normalised two-dimensional array of correlation values, theresulting normalised two-dimensional array of correlation values, 900-1or 900-2, indicates the response of the retina to the light stimulus asa function of location in the scanned region R of the retina 10 andtime.

To allow the response of the retina to the light stimulus to beillustrated in a form that may be more useful for a healthcarepractitioner such as an ophthalmologist, the correlation calculatormodule 120-1 may, as shown in step S50 of FIG. 5 , convert thetwo-dimensional array of correlation values (or the normalisedtwo-dimensional array of correlation values, as the case may be) to asequence of correlation values by replacing each of the one-dimensionalarrays of correlation values in the two-dimensional array 800, 900-1 or900-2 (each of the one-dimensional arrays indicating the response of theretina 10 to the light stimulus as a function of location in the scannedregion R of the retina 10) with a single respective value that is anaverage of the correlation values in the one-dimensional array, thesequence of correlation values indicating a response of the scannedregion R of the retina 10 to the light stimulus as a function of time.

In step S60 of FIG. 5 , the image data generator module 130 uses thesequence of correlation values generated in step S50 to generate imagedata defining an image which indicates the response of the retina 10 tothe light stimulus.

The image data may, for example, define an image which indicates thecalculated response of the scanned region R of the retina 10 to thelight stimulus as a function of time; in other words, the strength ofthe correlation of the change in OCT intensity with the time elapsedsince the corresponding stimulus was applied. An example of such animage is shown in FIG. 7 , where the solid response curve illustratesthe strength of the calculated correlation of the change in OCTintensity with the time elapsed since the corresponding stimulus wasapplied. This data may, as also illustrated in FIG. 7 , be augmented byadditional plotted curves (or coloured bands) defining upper and lowerlimits, which may be created, for example, by computing a confidenceinterval from functional OCT data recorded from a set of healthy eyes.Diseased eyes would be expected to fall outside of these limits, therebyaiding the healthcare practitioner to diagnose potential loss offunction. A typical representation may show a green band for the 95%confidence interval as computed from functional OCT data acquired from aset of healthy eyes. Alternatively, bands or limits may be displayedthat have been computed from functional OCT data acquired from eyes withspecific diseases.

Additionally or alternatively, the image data may define an image whichindicates one or more properties of a curve which defines the responseof the scanned region R of the retina 10 to the light stimulus as afunction of time, for example the (solid) response curve shown in FIG. 7. An indicated property of the response curve may (depending on theshape of the curve) be the presence of a change from a predeterminedfirst value to at least a predetermined second (higher or lower) value,the presence of one or more maxima or minima in the response curve, orthe absence of a significant change in the calculated correlationstrength indicated by the response curve (e.g. as determined by thecalculated correlation strength remaining within predefined upper andlower limits), for example. The latter property, i.e. no change in theresponse curve (other than any noise that may be present) might beexpected to be observed in data from diseased eyes, which show little orno response to light stimulation. The indicated property of the responsecurve may alternatively be data (referred to herein as a “marker”) whichquantifies one or more of the aforementioned features of the responsecurve. For example, where there is an extremum (a maximum or a minimum)in the response curve, the image defined by the image data may providean indication of the time to the extremum since the stimulus was appliedand/or an indication of the amplitude of the extremum relative to apredefined reference (e.g. zero correlation strength). Where there is asecond extremum in the response curve (which may be the same or adifferent kind of extremum than the first extremum), the image definedby the image data may additionally or alternatively provide anindication of the time to the second extremum since the stimulus wasapplied and/or an indication of the amplitude of the second extremumrelative to the predefined reference, and/or an indication of thedifference in amplitude between the first and second extrema, forexample. The indication(s) (marker(s)) may be provided in the form ofone or more numerical values, or as a classification of each value intoone of a number of predefined numerical ranges, for example. Eachindication may be augmented, in the image that is defined by the imagedata, with a comment or a colour to indicate whether it is within anormal (healthy) range, or within an abnormal range of values that isindicative of a diseased state.

The image data discussed above represents data that has been aggregatedover the whole of each B-scan, and thus over the whole of the scannedregion R. As a further alternative, respective correlations may becomputed for each of a plurality of different sections of the scannedregion R of the retina (with each section comprising a differentrespective set of A-scans), and these correlations may be mapped to anen-face representation of the retina, either as a diagram or as aretinal image such as a fundus image, a scanning laser ophthalmoscope(SLO) image or an en-face OCT image, for example. In other words, therolling window correlation described above may be calculated separatelyfor each of two or more sections of the sequence of B-scans 500, whichare obtained by dividing each B-scan in the sequence of B-scan 500 inthe same way, into two or more sets of adjacent A-scans, andconcatenating the resulting corresponding sets of A-scans to obtain therespective sections of the sequence of B-scans 500, as illustrated inFIG. 8 (where the B-scans are divided into three equally-sized sectionsin the A-scan direction, by way of an illustrative example, althoughthere may more generally be more or fewer sections, which need not havethe same number of A-scans).

The image data may thus additionally or alternatively define an imagewhich indicates a spatial variation, in the scanned region R of theretina 10, of the one or more properties of the response curve mentionedabove (for example), the spatial variation being overlaid on an en-facerepresentation of at least a portion the retina which includes thescanned region R. The correlations calculated for the different sectionsof the scanned region R may be coloured in accordance with anyappropriate colour scheme to indicate one or more of the following, forexample: (i) the value of one of the markers in each of the sections;(ii) which of a predefined set of intervals the marker in each of thesections belongs to, based on a reference database, e.g. green for apart of the scanned region of the retina that has provided a signalwhich corresponds to a marker “amplitude of the difference between thefirst and second peak” whose value is within the 95% confidence intervalof a population of healthy eyes; (iii) the percentage of the correlationvalues on the response curve that adheres to the confidence interval ofa reference set of either healthy eyes or eyes with a specific disease;or (iv) aggregate values from the response curve, such as maximum,minimum, mean or median over time, where a darker hue or more red colouris higher than a lighter hue or more blue/green colour, for example.

FIG. 9 is an example illustration of an image indicating respectivecorrelation strengths calculated for each of four different sections,R₁, R₂, R₃, and R₄, of the scanned region R of the retina 10 (using fourcorresponding sections of the sequence of B-scans 500), which areoverlaid on a representation 1000 of the retina 10. Where the scan hastaken place, different colours and hues may be used to indicate one ofoptions (i) to (iv) listed above, for example. In the example of FIG. 9, the scan pattern on the retina resembles the shape of a figure of 8,although other scan patterns could alternatively be used.

The image which indicates the overlay of the spatial variation (in thescanned region R) of the one or more properties of the response curveonto an en-face representation may be turned into an animation byshowing how the correlation strength varies over time at each scanlocation in the scanned region R shown in the image. Colours and hue maybe used to represent the amplitude of the correlation strength and signby converting either the absolute strength or the normalised strengthvalues to different hues, e.g. darker hues to illustrate a strongersignal, and different colours, e.g. blue for positive correlation andred for negative correlation, for example.

The image data may define an image which is indicative of retinalresponses derived from two separate functional OCT data sets, forexample first set of functional OCT data that has been acquired from aneye, and a second set of functional OCT data that has subsequently beenacquired from the same eye, the image allowing corresponding responsesof the retina to be compared to one another. The image data generator130 may generate image data that allows two main forms of results to bedisplayed, as follows: (i) retinal responses based on the first andsecond sets of functional OCT data, which may be presented in the same(or same kind of) graph or table in order to enable the healthcarepractitioner to see the absolute values ‘side by side’—this isapplicable to both the correlation strength variations over time (whichmay, for example, be plotted on a graph) and the derived markers (whichmay, for example, be presented in columns or rows of a table); and (ii)the difference or a ratio between the retinal responses based on thefirst and second sets of functional OCT data. Colour and hue may be usedto show the magnitude and sign (e.g. red for negative and blue forpositive) of the difference, for example. An example of a functional OCTreport defined by such image data is illustrated in FIG. 10 .

Embodiment 2

In the first example embodiment, the correlation calculator module 120-1is configured to calculate the rolling window correlation between thesequence of B-scans 500 and the sequence S of stimulus indicatorsreceived from the OCT imaging device 200, and to subsequently processthe resulting three-dimensional array 700 of correlation values (in stepS40 of FIG. 5 ) so as to generate a two-dimensional array 800 ofcorrelation values, by taking the average of the correlation values inthe depth (d) direction. However, the averaging operation may, as in thepresent example embodiment, alternatively be performed on the B-scansprior to their correlation with the sequence S of stimulus indicators,thereby simplifying and speeding up the correlation calculation.

FIG. 11 is a schematic illustration of an apparatus 100-2 according tothe second example embodiment, which comprises, in addition to thereceiver module 110 and the image data generator module 130 that are thesame as those in apparatus 100-1, a B-scan processing module 115 and acorrelation calculator module 120-2. The apparatus 100-2 of the presentexample embodiment thus differs from the apparatus 100-1 of the firstexample embodiment only by comprising the B-scan processing module 115,and the correlation calculator module 120-2, whose functionality differsfrom that of the correlation calculator module 120-1 of the firstexample embodiment (as explained in more detail below). The followingdescription of the second example embodiment will therefore focus onthese differences, with all other details of the first exampleembodiment, which are applicable to the second example embodiment, notbeing repeated here for sake of conciseness. It should be noted that thevariations and modifications which may be made to the first exampleembodiment, as described above, are also applicable to the secondembodiment. It should also be noted that one or more of the illustratedcomponents of the apparatus 100-2 may be implemented in the form of aprogrammable signal processing hardware as described above withreference to FIG. 2 , or alternatively in the form of non-programmablehardware, such as an application-specific integrated circuit (ASIC).

FIG. 12 is a flow diagram illustrating a method by which the apparatus100-2 of the second example embodiment processes functional OCT data togenerate an indication of a response of the retina 10 to the lightstimulus.

In step S10 of FIG. 12 (which is same as step S10 in FIG. 3 ), thereceiver module 110 receives from the OCT imaging device 200, as thefunctional OCT image data: (i) OCT image data (specifically, in the formof a sequence of B-scans 500) that has been generated by the OCT imagingdevice 200 repeatedly scanning the scanned region R of the retina 10over a time period T; and (ii) stimulus data defining the sequence of sstimulus indicators, each indicative of a stimulation of the retina bythe light stimulus in a respective time interval, T/s, of a sequence oftime intervals that spans the time period T.

In step S15 of FIG. 12 , the B-scan processing module 115 converts thesequence of B-scans 500 received by the receiver module 110 in step S10into a sequence of reduced B-scans 550, by replacing each A-scan in thesequence of A-scans forming each B-scan 400 with a respective averagevalue of A-scan elements of the A-scan, as illustrated in FIG. 13 .

In step S20-2 of FIG. 12 , the correlation calculator module 120-2calculates the rolling window correlation between reduced B-scans in thesequence of reduced B-scans 550 and stimulus indicators s₁, s₂, s₃ . . .in the sequence S of stimulus indicators by calculating, for each of thestimulus indicators, a product of the stimulus indicator and arespective windowed portion of the sequence of reduced B-scans 550,which may begin with a reduced B-scan that is based on a B-scan of thesequence of B-scans 500 which has been generated by the OCT imagingdevice 200 while the retina 10 was being stimulated in accordance withthe stimulus indicator, and include a predetermined number of subsequentreduced B-scans in the sequence of reduced B-scans 550.

In step S30 of FIG. 12 , the correlation calculator module 120-2combines the calculated products to generate, as the indication of theresponse of the retina 10 to the light stimulus, a two-dimensional arrayof correlation values (as shown at 800 in FIG. 6(a)) indicating theresponse of the retina 10 to the light stimulus as a function oflocation in the scanned region R of the retina 10 and time.

The two-dimensional array 800 of correlation values may be processed bythe image data generator module 130 to generate image data in the sameway as in the first example embodiment, and/or the correlationcalculator module 120-2 may pre-process the two-dimensional array 800 ofcorrelation values and/or convert the two-dimensional array ofcorrelation values (or the normalised two-dimensional array ofcorrelation values, as the case may be) to a sequence of correlationvalues in the same way as the correlation calculator module 120-1 of thefirst example embodiment. The sequence of correlation values may furtherbe processed by the image data generator module 130 to generate imagedata in the same way as in step S60 of the first example embodiment.

Embodiment 3

The processing of functional OCT data that is performed by the apparatus100-1 of the first example embodiment allows an indication of thefunctional response of a scanned region R of the retina 10 to beobtained, based on a correlation which is computed for the whole retinaldepth covered by the scan. However, it may be valuable for determiningdisease diagnosis, for example, to be able to generate an indication ofthe individual functional responses of one or more retinal layerscorresponding to different cell types (e.g. photoreceptors, retinalpigment epithelium, retinal nerve fiber layer, etc.). Such enhancedfunctionality is provided by the apparatus 100-3 of the third exampleembodiment, which will now be described with reference to FIGS. 14 to 16.

FIG. 14 is a schematic illustration of an apparatus 100-3 for processingfunctional OCT image data to generate an indication of the individualresponses of one or more layers of the retina to the light stimulus,according to the third example embodiment. The apparatus 100-3 comprisesthe same receiver module 110 as the first and second exampleembodiments, a B-scan processing module 117, a correlation calculatormodule 120-3, and an image generator module 130 which is the same asthat of the first and second example embodiments. It should also benoted that one or more of the illustrated components of the apparatus100-3 may be implemented in the form of a programmable signal processinghardware as described above with reference to FIG. 2 , or alternativelyin the form of non-programmable hardware, such as anapplication-specific integrated circuit (ASIC). Processing operationsperformed by the apparatus 100-3 will now be described with reference toFIG. 15 .

FIG. 15 is a flow diagram illustrating a method by which the apparatus100-3 of the third example embodiment processes functional OCT data togenerate an indication of the response of one or more layers of theretina 10 to the light stimulus.

In step S10 of FIG. 15 , the receiver module 110 receives functional OCTimage data from the OCT imaging device 200. Step S10 in FIG. 15 is thesame as step S10 in FIG. 3 , and will therefore not be described infurther detail here.

In step S12 of FIG. 15 , the B-scan processing module 117 identicallysegments each B-scan 400 in the sequence of B-scans 500 into a pluralityof B-scan layers, so that each B-scan layer comprises respectivesections of the A-scans forming the B-scan 400. In other words, asillustrated in FIG. 16 , the B-scan processing module 117 divides afirst B-scan 400-1 in the sequence of B-scans 500 into a plurality oflayers (or segments) 400-1 a, 400-1 b and 400-1 c in the depthdirection, so that each layer comprises a respective set of a A-scansections, divides a second B-scan 400-2 in the sequence of B-scans 500into a plurality of layers (or segments) 400-2 a, 400-2 b and 400-2 c inthe depth direction, so that each layer comprises a respective set of aA-scan sections, and so on. It should be noted that the segmentation ofthe B-scans by the B-scan processing module 117 into three equal layersin FIG. 16 is given by way of example only, and that the B-scans may besegmented into a greater or smaller number of B-scan layers. It shouldalso be noted that the number of A-scan elements in the columns of theB-scan layers need not be the same; in other words, the B-scan layersmay have different respective thicknesses.

The B-scan processing module 117 further concatenates correspondingB-scan layers (i.e. B-scan layers from different B-scans, which B-scanlayers contain respective sets of OCT measurement results derived fromthe same range of depths from the retinal surface) from the segmentedB-scans to generate sequences of concatenated B-scan layers. Thus, asillustrated in FIG. 16 , the B-scan processing module 117 concatenatesB-scan layers 400-1 a, 400-2 a, 400-3 a, . . . etc. to generate a firstsequence of concatenated B-scan layers, 450 a, which corresponds to afirst layer of the retina 10, concatenates B-scan layers 400-1 b, 400-2b, 400-3 b, . . . etc. to generate a second sequence of concatenatedB-scan layers, 450 b, which corresponds to a second (deeper) layer ofthe retina 10, and concatenates B-scan layers 400-1 c, 400-2 c, 400-3 c,. . . etc. to generate a third sequence of concatenated B-scan layers,450 c, which corresponds to a third (yet deeper) layer of the retina 10.Each of the sequences of concatenated B-scan layers thus forms athree-dimensional array of A-scan elements, which corresponds to arespective layer of the retina 10.

In step S20-3 of FIG. 15 , the correlation calculator module 120-3calculates, for each of at least one sequence of concatenated B-scanlayers of the sequences of concatenated B-scan layers generated in stepS12 of FIG. 15 , a respective rolling window correlation betweenconcatenated B-scan layers in the sequence of concatenated B-scan layersand stimulus indicators (s₁, s₂, s₃) in the sequence S of stimulusindicators, specifically by calculating, for each stimulus indicator, aproduct of the stimulus indicator and a respective windowed portion ofthe sequence of concatenated B-scan layers, comprising a B-scan layer ofthe B-scan layers which is based on a B-scan 400 which has beengenerated by the OCT imaging device 200 while the retina 10 was beingstimulated in accordance with the stimulus indicator, and thepredetermined number, b_(lag), of subsequent B-scan layers in thesequence of concatenated B-scan layers.

In step S30 of FIG. 15 , for each of the at least one sequence ofconcatenated B-scan layers, the correlation calculator module 120-3combines the products calculated in step S20-3 to generate a respectivethree-dimensional array of values (“response volume”) that provides anindication of a response of the respective layer of the retina (10) tothe light stimulus.

Each resulting three-dimensional array of correlation values may furtherbe processed by the correlation calculator module 120-3, and the resultsof those further processing operations may be used by the image datagenerator module 130 to generate image data defining an image whichindicates the response of the corresponding layer of the retina to thelight stimulus for display to a user of the apparatus 100-3, using thefurther processing operations that have been explained in the abovedescription of the first embodiment, with reference to FIG. 5 .

More particularly, the response volume corresponding to each retinallayer may be reduced to a two-dimensional response image for easiervisualisation, by taking the average in the depth (d) direction, i.e.one value per A-scan per lag time point. Thus, the correlationcalculator module 120-3 may convert each three-dimensional array ofcorrelation values, which is a/3×b_(lag)×d pixels in size in the presentexample embodiment, into a respective two-dimensional array ofcorrelation values, which is a/3×b_(lag) pixels in size, by replacingeach one-dimensional array of correlation values in thethree-dimensional array, which one-dimensional array has been calculatedusing sections of A-scans that are identically located in respectiveB-scans of the sequence of B-scans, with a single value that is anaverage of the correlation values in the one-dimensional array. Thus,each array element of the one-dimensional array is calculated on thebasis of a corresponding element of an A-scan. The two-dimensional arrayof correlation values indicates the response of the corresponding layerof the retina 10 to the light stimulus as a function of location alongthe scanned region R of the retina 10 (i.e. as a function of positionalong the line defining the scan pattern) and time.

The image data generator module 130 may use at least one of thetwo-dimensional arrays of correlation values to generate image datadefining an image which indicates the response, to the light stimulus,of a respective layer of the retina 10 corresponding to each of the atleast one of the two-dimensional arrays as a function of location in thescanned region R of the retina 10 and time. However, it may bepreferable to pre-process at least some of the two-dimensional arrays ofcorrelation values prior to image data generation (or prior to thealternative further processing operation described below), in order toaccentuate the time-dependent variability of the signal, i.e. thevariation of the retinal layer response to light stimulation over time.Such pre-processing may be desirable in cases where the responsevariability in the A-scan direction is greater than in the time lagdirection.

The correlation calculator module 120-3 may pre-process one or more ofthe two-dimensional arrays of correlation values, each comprising asequence of b_(lag) one-dimensional arrays, each indicating the responseof the corresponding layer of the retina to the light stimulus as afunction of location in the scanned region R of the retina 10, togenerate a normalised two-dimensional array of correlation values. Thecorrelation calculator module 120-3 may generate the normalisedtwo-dimensional array of correlation values by subtracting the firstone-dimensional array in the sequence of one-dimensional arrays fromeach remaining one-dimensional array in the sequence of one-dimensionalarrays. Alternatively, the correlation calculator module 120-3 maygenerate a normalised two-dimensional array of correlation values bycalculating an array of averaged correlation values, such that eachaveraged correlation value in the array of averaged correlation valuesis an average (mean) of the correlation values that are correspondinglylocated in the sequence of one-dimensional arrays, and subtracting thecalculated array of averaged correlation values from each of theone-dimensional arrays in the sequence of one-dimensional arrays (inother words, performing a vector subtraction of the calculated array ofaveraged correlation values from each of the one-dimensional arrays). Inboth of these alternative ways of calculating normalised two-dimensionalarray of correlation values, the resulting normalised two-dimensionalarray of correlation values indicates the response of the correspondinglayer of the retina to the light stimulus as a function of location inthe scanned region R of the retina 10 and time. The image data generatormodule 130 may use each normalised two-dimensional array of correlationvalues to generate image data defining an image that indicates theresponse of the corresponding layer of the retina 10 to the lightstimulus as a function of location in the scanned region R of the retina10 and time.

To allow the response of one or more layers of the retina 10 to thelight stimulus to be illustrated in a form that may be more useful for ahealthcare practitioner or other user, the correlation calculator module120-3 may convert the two-dimensional array of correlation values (orthe normalised two-dimensional array of correlation values, as the casemay be) corresponding to each of one or more of the retinal layers to asequence of correlation values by replacing each of the one-dimensionalarrays of correlation values in the two-dimensional array (each of theone-dimensional arrays indicating the response of the correspondinglayer of the retina 10 to the light stimulus as a function of locationalong the scanned region R of the retina 10) with a single respectivevalue that is an average of the correlation values in theone-dimensional array, each sequence of correlation values indicating aresponse of the respective layer of the retina 10 in the scanned regionR to the light stimulus as a function of time.

The image data generator module 130 may use one or more of the sequencesof correlation values to generate image data defining an image thatindicates the response of the respective one or more layers of theretina 10 in the scanned region R of the retina to the light stimulus.

Similar to the first and second example embodiments described above, theimage data generator module 130 may use one or more sequences ofcorrelation values to generate an image which indicates at least one of:the response of the respective one or more layers of the retina 10 inthe scanned region R to the light stimulus as a function of time; one ormore properties of a respective one or more curves defining the responseof the respective one or more layers of the retina 10 in the scannedregion R to the light stimulus as a function of time; and a spatialvariation, in the scanned region R of the retina 10, of one or moreproperties of the respective one or more curves defining the response ofthe respective one or more layers of the retina 10 in the scanned regionR to the light stimulus as a function of time, the spatial variationbeing overlaid on an en-face representation of at least a portion theretina 10 which includes the scanned region R.

Embodiment 4

In the third example embodiment, the correlation calculator module 120-3is, in one configuration, configured to calculate, for each of at leastone sequence of concatenated B-scan layers of the concatenated sequencesof B-scan layers, a respective rolling window correlation between thesequence of concatenated B-scan layers and the sequence S of stimulusindicators received from the OCT imaging device 200, and to subsequentlyprocess the resulting three-dimensional array of correlation values soas to generate a two-dimensional array of correlation values, by takingan average of the correlation values in the depth (d) direction.However, the averaging operation may, as in the present exampleembodiment, alternatively be performed on the one or more of thesequences of concatenated B-scan layers prior to their correlation withthe sequence S of stimulus indicators, thereby simplifying and speedingup the correlation calculation.

FIG. 17 is a schematic illustration of an apparatus 100-4 according tothe fourth example embodiment, which comprises, in addition to thereceiver module 110 and the image data generator module 130 that are thesame as those in apparatuses 100-1, 100-2 and 100-3 of the foregoingexample embodiments, a B-scan processing module 118 and a correlationcalculator module 120-4, which are described in detail below. The B-scanprocessing module 118 has functionality in common with that the B-scanprocessing module 117 of the third example embodiment (which will not bedescribed here again), as well as some further functionality which isdescribed below. It should also be noted that one or more of theillustrated components of the apparatus 100-4 may be implemented in theform of a programmable signal processing hardware as described abovewith reference to FIG. 2 , or alternatively in the form ofnon-programmable hardware, such as an application-specific integratedcircuit (ASIC).

FIG. 18 is a flow diagram illustrating a method by which the apparatus100-4 of the fourth example embodiment processes functional OCT data togenerate an indication of a response of the retina 10 to the lightstimulus.

In step S10 of FIG. 18 , the receiver module 110 receives the functionalOCT image data from the OCT imaging device 200. Step S10 in FIG. 18 isthe same as step S10 in FIG. 3 , and will therefore not be described infurther detail here.

In step S12 of FIG. 18 , the B-scan processing module 118 identicallysegments each B-scan 400 in the sequence of B-scans 500 into a pluralityof B-scan layers, so that each B-scan layer comprises respectivesections of the A-scans forming the B-scan 400. Step S12 in FIG. 18 isthe same as step S12 in FIG. 15 , and will therefore not be described infurther detail here. As in the third example embodiment, each of thesequences of concatenated B-scan layers forms a three-dimensional arrayof A-scan elements, which corresponds to a respective later of theretina 10.

In step S17 of FIG. 18 , the B-scan processing module 118 converts eachof at least one of the sequences of concatenated B-scan layers into arespective sequence of concatenated reduced B-scan layers, by replacing,for each B-scan layer in each of the at least one sequence ofconcatenated B-scan layers, the sections of the A-scans forming theB-scan layer with corresponding values of an average of A-scan elementsin the sections of the A-scans. For example, in the illustrative exampleof FIG. 16 , the B-scan processing module 118 converts thethree-dimensional array formed by the first sequence of concatenatedB-scan layers, 450 a, into a two-dimensional array, by replacing thefirst column of B-scan layer (or segment) 400-1 a, comprising A-scanelements a1 and a2, with a single value that is an average of a1 and a2,with the remaining columns of B-scan segment 400-1 a, and the otherB-scan segments 400-1 b, 400-1 c, etc. of the first sequence ofconcatenated B-scan layers 450 a are processed in the same way. TheB-scan processing module 118 may likewise process the second sequence ofconcatenated B-scan layers 450 b and/or the third sequence ofconcatenated B-scan layers 450 c in addition to, or alternatively to,the first sequence of concatenated B-scan layers 450 a. Thus, the B-scanprocessing module 118 can convert each of one or more of thethree-dimensional arrays of OCT measurement values shown in the exampleof FIG. 16 , each of which is a/3×b_(lag)×d pixels in size, into arespective two-dimensional array of values, which is a/3×b_(lag) pixelsin size.

In step S20-4 of FIG. 18 , the correlation calculator module 120-4calculates, for each of at least one sequence of concatenated reducedB-scan layers of the sequences of concatenated reduced B-scan layersgenerated in step S17 of FIG. 18 , a respective rolling windowcorrelation between reduced B-scan layers in the sequence ofconcatenated reduced B-scan layers and stimulus indicators (s₁, s₂, s₃)in the sequence S of stimulus indicators, specifically by calculating,for each stimulus indicator, a product of the stimulus indicator and arespective windowed portion of the sequence of concatenated reducedB-scan layers comprising a reduced B-scan layer which is based on aB-scan that has been generated by the OCT imaging device 200 while theretina 10 was being stimulated in accordance with the stimulusindicator, and the predetermined number, b_(lag), of subsequent reducedB-scan layers in the sequence of concatenated reduced B-scan layers.

In step S30 of FIG. 18 , for each of the at least one sequence ofconcatenated reduced B-scan layers, the correlation calculator module120-4 combines the products calculated in step S20-4 to generate arespective two-dimensional array of values (“response area”) thatprovides an indication of a response of a layer of the retinacorresponding to the sequence of concatenated reduced B-scan layers tothe light stimulus as a function of location in the scanned region R ofthe retina 10 and time.

Each resulting two-dimensional array of correlation values may furtherbe processed by the correlation calculator module 120-4 in the same wayas the two-dimensional array(s) of correlation values is/are processedby the correlation calculator module 120-3 in the third exampleembodiment described above.

Thus, the image data generator module 130 may use at least one of thetwo-dimensional arrays of correlation values to generate image datadefining an image which indicates the response, to the light stimulus,of a respective layer of the retina 10 corresponding to each of the atleast one of the two-dimensional arrays as a function of location in thescanned region R of the retina 10 and time. However, it may bepreferable to pre-process at least some of the two-dimensional arrays ofcorrelation values prior to image data generation (or prior to thealternative further processing operation described below), in order toaccentuate the time-dependent variability of the signal, i.e. thevariation of the retinal layer response to light stimulation over time.Such pre-processing may be desirable in cases where the responsevariability in the A-scan direction is greater than in the time lagdirection.

The correlation calculator module 120-4 may pre-process one or more ofthe two-dimensional arrays of correlation values, each comprising asequence of b_(lag) one-dimensional arrays, each array indicating theresponse of the corresponding layer of the retina 10 to the lightstimulus as a function of location in the scanned region R of the retina10, to generate a normalised two-dimensional array of correlationvalues. The correlation calculator module 120-4 may generate anormalised two-dimensional array of correlation values (indicating theresponse of the corresponding layer of the retina 10 to the lightstimulus as a function of location in the scanned region R of the retina10 and time) using one of the processes described in the third exampleembodiment, for example. The image data generator module 130 may useeach normalised two-dimensional array of correlation values to generateimage data defining an image that indicates the response of thecorresponding layer of the retina 10 to the light stimulus as a functionof location in the scanned region R of the retina 10 and time.

To allow the response of one or more layers of the retina to the lightstimulus to be illustrated in a form that may be more useful for ahealthcare practitioner such as an ophthalmologist, the correlationcalculator module 120-4 may convert the two-dimensional array ofcorrelation values (or the normalised two-dimensional array ofcorrelation values, as the case may be) corresponding to each of one ormore of the retinal layers to a sequence of correlation values byreplacing each of the one-dimensional arrays of correlation values inthe two-dimensional array (each of the one-dimensional arrays indicatingthe response of the corresponding layer of the retina 10 to the lightstimulus as a function of location in the scanned region R of the retina10) with a single respective value that is an average of the correlationvalues in the one-dimensional array, each sequence of correlation valuesindicating a response of the respective layer of the retina 10 in thescanned region to the light stimulus as a function of time.

The image data generator module 130 may use one or more of the sequencesof correlation values to generate image data defining an image thatindicates the response of the respective one or more layers of theretina 10 in the scanned region R of the retina to the light stimulus.

Similar to the third example embodiment described above, the image datagenerator module 130 may use one or more sequences of correlation valuesto generate an image which indicates at least one of: the response ofthe respective one or more layers of the retina 10 in the scanned regionR to the light stimulus as a function of time; one or more properties ofa respective one or more curves defining the response of the respectiveone or more layers of the retina 10 in the scanned region R to the lightstimulus as a function of time; and a spatial variation, in the scannedregion R of the retina 10, of one or more properties of the respectiveone or more curves defining the response of the respective one or morelayers of the retina 10 in the scanned region R to the light stimulus asa function of time, the spatial variation being overlaid on an en-facerepresentation of at least a portion the retina 10 which includes thescanned region R.

Embodiment 5

FIG. 19 is a schematic illustration of an apparatus 100-5 according to afifth example embodiment, which is configured to process functional OCTimage data to generate an indication of how well a retina 10 of asubject's eye 20 responds to a flickering light stimulus. The functionalOCT data processed by the apparatus 100-5 is acquired by the OCT imagingdevice 200, which has already been described above.

The light stimulus may, as in the present example embodiment, comprise afull-field light stimulus (or flash), which provides substantiallyuniform illumination (at wavelengths in the visible spectrum betweenabout 380 and 740 nm in the present example, although other wavelengthscould alternatively or additionally be used) that fills the whole visualfield of the subject. The light stimulus generator 220 may, for example,comprise a light-emitting diode (LED) or other optical emitter forgenerating the light stimuli. The flashes that the light stimulusgenerator 220 emits may, as in the present example embodiment, give riseto a random (or pseudo-random) stimulation of the retina over time. Inother words, the light stimulus generator 220 may emit light flashesthat are randomly or pseudo-randomly distributed in time, so that thesubject cannot (subconsciously) learn to anticipate upcoming flashes,thereby allowing a more accurate functional response to the subject'sretina 10 to light stimulation to be measured.

It should be noted, however, that the light stimulus need not be afull-field stimulus, and may alternatively stimulate only a portion ofthe retina, which may be illuminated in accordance with a structuralscan pattern (e.g. an annulus, a hypotrochoid, or Lissajous figure, forexample) by the ophthalmic scanner of the OCT imaging device 200.

As illustrated in FIG. 19 , the apparatus 100-5 of the present exampleembodiment comprises a receiver module 110, a correlation calculatormodule 120-5, a response generator module 125-5 and, optionally, animage data generator module 130, which are communicatively coupled (e.g.via a bus 140) so as to be capable of exchanging data with one anotherand with the OCT imaging device 200. The receiver module 110 and theimage data generator module 130 are the same as those in the firstexample embodiment.

As with the preceding example embodiments, the programmable signalprocessing hardware 300 described above with reference to FIG. 2 may beconfigured to process functional OCT data using the techniques describedherein and, in particular, function as the receiver module 110, thecorrelation calculator module 120-5, the response generator module 125-5and the (optional) image data generator module 130 of the fifth exampleembodiment. It should be noted, however, that the receiver module 110,the correlation calculator module 120-5, the response generator module125-5 and/or the image data generator module 130 may alternatively beimplemented in non-programmable hardware, such as anapplication-specific integrated circuit (ASIC).

In the present example embodiment, a combination 370 of the hardwarecomponents shown in FIG. 2 , comprising the processor 320, the workingmemory 330 and the instruction store 340, is configured to performfunctions of the receiver module 110, the correlation calculator module120-5, the response generator module 125-5 and the image data generatormodule 130 that are described below.

FIG. 20 is a flow diagram illustrating a method performed by theprocessor 320, by which the processor 320 processes functional OCT data,which has been acquired by the OCT imaging device 200 scanning thesubject's retina 10 while the retina 10 is being repeatedly stimulatedby the light stimulus, to generate an indication of a response of theretina 10 to the light stimulus.

In step S10 of FIG. 20 , the receiver module 110 receives from the OCTimaging device 200, as the functional OCT image data: (i) OCT image datathat has been generated by the OCT imaging device 200 repeatedlyscanning a scanned region R of the retina 10 over a time period T; and(ii) stimulus data defining a sequence of s stimulus indicators, eachstimulus indicator being indicative of a stimulation of the retina 10 bythe light stimulus in a respective time interval, T/s, of a sequence oftime intervals that spans the time period T.

The received OCT image data may, as in the present example embodiment,comprise a sequence of b B-scans, which has been generated by the OCTimaging device 200 repeatedly scanning the scanned region R of theretina 10 over the time period T. Referring back to FIG. 4 , this figureillustrates functional OCT image data acquired by the receiver module110 in step S10 of FIG. 20 . As illustrated in FIG. 4 , each B-scan 400in the sequence of B-scans can be represented as a 2D image made up of aA-scans (vertical lines). Each A-scan comprises a one-dimensional arrayof d pixels, where the pixel value of each pixel represents acorresponding OCT measurement result, and the location of each pixel inthe one-dimensional array is indicative of the OCT measurement locationin the axial direction of the OCT imaging device 200, at which locationthe corresponding pixel value was measured. The OCT image data can thusbe represented as a three-dimensional pixel array 500, which is a×b×dpixels in size.

It should be noted that each A-scan in the B-scan 400 may be an averageof a number of adjacent A-scans that have been acquired by the OCTimaging device 200. In other words, the OCT imaging device 200 mayacquire A-scans having lateral spacing (e.g. along the surface of theretina) which is smaller than the optical resolution of the OCT imagingdevice 200, and average sets of adjacent A-scans to generate a set ofaveraged A-scans which make up a B-scans displaying improvedsignal-to-noise.

The OCT imaging device 200 generates the OCT image data by scanning alaser beam across the scanned region R of the retina 10 in accordancewith a predetermined scan pattern, acquiring the A-scans that are tomake up each B-scan 400 as the scan location moves over the scannedregion R. The shape of the scan pattern on the retina 10 is not limited,and is usually determined by a mechanism in the OCT imaging device 200that can steer the laser beam generated by the OCT measurement module210. In the present example embodiment, galvanometer (“galvo”) motors,whose rotational position values are recorded, are used to guide thelaser beam during the acquisition of the OCT data. These positions canbe correlated to locations on the retina 10 in various ways, which willbe familiar to those versed in the art. The scan pattern may, forexample, trace out a line, a curve, or a circle on the surface of theretina 10, although a lemniscate scan pattern is employed in the presentexample embodiment. The A-scans acquired during each full period of thescan pattern form one B-scan. In the present example embodiment, all ofthe b B-scans are recorded in the time period T, such that the time perB-scan is T/b, and the scan pattern frequency is b/T.

During the time period T, while the OCT image data is being generated bythe OCT imaging device 200, a stimulus is shown to the subject, whichcan be a full-field stimulus (substantially the same brightness valueover the whole visual field), as in the present example embodiment, or aspatial pattern, where the visual field is divided into e.g. squares,hexagons or more complicated shapes. In the case of a full-fieldstimulus, at any point in time, the brightness can be denoted, forexample, as either “1” (full brightness) or as “−1” (darkness, with nostimulus having been applied). The time period Tis divided into asequence of s time intervals (corresponding to the “stimulus positions”referred to herein), each of size T/s and, for each time interval, thereis an associated stimulus indicator (s₁, s₂, s₃ . . . ) which isindicative of a stimulation of the retina 10 by the light stimulus inthe respective time interval T/s. Thus, each stimulus indicator in thesequence of stimulus indicators may take a value of either 1 or −1(although the presence or absence of the stimulus may more generally bedenoted by n and −n, where n is an integer). The concatenation of thestimulus indicator values that are indicative of the stimulation of theretina 10 during OCT image data generation is referred to herein as asequence S of stimulus indicators. One choice for S is an m-sequence,which is a pseudo-random array. In alternative embodiments, in whichthere is a spatial pattern to the stimulus, each individual field caneither display a completely different m-sequence, or a version of onem-sequence that is (circularly) delayed by a specific time, or aninversion of one m-sequence (i.e. when one field shows a 1, anothershows a −1 and vice versa). As noted above, the receiver module 110 isconfigured to receive stimulus data defining the sequence S of stimulusindicators s₁, s₂, s₃, etc. The receiver module 110 may, for example,receive information defining the sequence S of stimulus indicatorsitself, or alternatively information that allows the sequence S ofstimulus indicators to be constructed by the apparatus 100-5.

It should be noted that, although each stimulus indicator in thesequence S of stimulus indicators is indicative of whether or not theretina 10 was stimulated by the light stimulus in the corresponding timeinterval of duration T/s, the stimulus indicator is not so limited, andmay, in other example embodiments, be indicative of a change instimulation of the retina 10 by the light stimulus that occurs in arespective time interval of the sequence S of time intervals that spansthe time period T. For example, in the following description ofcorrelation calculations, each windowed portion of the sequence ofB-scans may be multiplied by −1 if the stimulus changes from +1 to −1 inthe associated time interval T/s, by +1 if the stimulus changes from −1to +1 in the associated time interval T/s, and by zero if the stimulusdoes not change in the time interval.

After at least some of the functional OCT data have been received by thereceiver module 110, the correlation calculator 120-5 begins tocalculate a rolling window correlation between a sequence of B-scansthat is based on the OCT image data and at least some of the stimulusindicators in the sequence S of stimulus indicators.

More particularly, the correlation calculator module 120-5 calculatesthe rolling window correlation by calculating, in step S20-5 of FIG. 20, for each of the stimulus indicators s₁, s₂, s₃, etc., a respectivecorrelation between stimulus indicators in a window comprising thestimulus indicator and a predetermined number of adjacent stimulusindicators, and B-scans of the sequence of B-scans 500 that are based ona portion of the OCT image data generated while the retina 10 was beingstimulated in accordance with the stimulus indicators in the window. Byway of an example, the correlation calculator module 120-5 of thepresent example embodiment calculates, for each of the stimulusindicators, a correlation between stimulus indicators in a windowedportion of the sequence S consisting of a stimulus indicator located ata predetermined sequence position in the windowed portion (e.g. thefirst stimulus indicator in the windowed portion), and a predeterminednumber of adjacent (e.g. subsequent) stimulus indicators, andcorresponding B-scans of the sequence of B-scans 500 that are based on aportion of the OCT image data generated while the retina 10 was beingstimulated in accordance with the stimulus indicators in the window.

As noted above, the intervals T/b and T/s are not necessarily equal, andthere are b/s B-scans per stimulus position/indicator, or s/b stimuliper B-scan. By way of an example, b/s=2 in the present exampleembodiment, so that two B-scans are generated by the OCT imaging device200 while the retina 10 is being stimulated, or is not being stimulated(as the case may be), in accordance with each stimulus indicator value.

FIG. 21 is a schematic illustration of functional OCT image dataacquired by the receiver module 110 in step S10 of FIG. 20 , and resultsof processing the functional OCT image data in the fifth exampleembodiment herein.

As illustrated in FIG. 21 , the correlation calculator module 120-5calculates a product of the value of the first stimulus indicator s₁ inthe first windowed portion of stimulus indicators (the first windowedportion further comprising stimulus indicators s₂, s₃ and s₄), which is−1 in the example of FIG. 21 , and each of the data elements in thefirst two B-scans of a first portion (or block) of the three-dimensionalarray of pixels 500, which portion is a×2×d pixels in size, the firsttwo B-scans having been generated by the OCT imaging device 200 whilethe retina 10 was not being stimulated, in accordance with the stimulusindicator (s₁) value “−1” applicable for the time interval from time t=0to t=T/s. The correlation calculator module 120-5 also calculates aproduct of the value of the second stimulus indicator s₂ in the firstwindowed portion of stimulus indicators, which is +1 in the example ofFIG. 21 , and each of the data elements in the second pair of B-scans ofthe first portion of the three-dimensional array of pixels 500, thesecond pair of B-scans having been generated by the OCT imaging device200 while the retina 10 was being stimulated, in accordance with thestimulus indicator (s₂) value “+1” applicable for the time interval fromtime t=T/s to t=2T/s. The correlation calculator module 120-5 similarlycalculates a product of the value of the third stimulus indicator s₃ inthe first windowed portion of stimulus indicators, which is also +1 inthe example of FIG. 21 , and each of the data elements in the third pairof B-scans of the first portion of the three-dimensional array of pixels500, the third pair of B-scans having been generated by the OCT imagingdevice 200 while the retina 10 was being stimulated, in accordance withthe stimulus indicator (s₃) value “+1” applicable for the time intervalfrom time t=2T/s to t=3T/s. Likewise, the correlation calculator module120-5 calculates a product of the value of the fourth stimulus indicators₄ in the first windowed portion of stimulus indicators, which is −1 inthe example of FIG. 21 , and each of the data elements in the fourthpair of B-scans of the first portion of the three-dimensional array ofpixels 500, the fourth pair of B-scans having been generated by the OCTimaging device 200 while the retina 10 was not being stimulated, inaccordance with the stimulus indicator (s₄) value “−1” applicable forthe time interval from time t=3T/s to t=4T/s. The number of stimulusindicators in the window is, of course, not limited to four, and ispreferably chosen so that the corresponding number of B-scans, b_(lag),generated by the OCT imaging device 200 corresponds to a period of nomore than about 1 second, as the use of greater values of b_(lag) maymake little or no improvement to the calculated retinal response, whilstmaking the calculation more demanding of computational resources. Theresult of multiplying each stimulus indicator in the window withrespective B-scans in the sequence of B-scans is represented by partialresponse block 600′-1 illustrated in FIG. 21 .

This multiplication process is repeated for the remaining stimulusindicators in the sequence S of stimulus indicators, with thecorrelation calculator module 120-5 moving the rolling window forward intime by one time interval T/s in each step of the process, so that itslides past the second stimulus indicator, s₁, in the sequence S ofstimulus indicators and covers the stimulus indicator immediatelyadjacent the right-hand boundary of the rolling window as it waspreviously positioned, and the product of the stimulus indicators andrespective B-scans in the sequence of B-scans 500 is calculated onceagain to generate another partial response block (600′-2, etc.) ofweighted B-scans. This procedure of sliding the rolling window forwardin time and calculating the product to obtain a block of weightedB-scans for each rolling window position is repeated until the rollingwindow reaches the end of the sequence S of stimulus indicators, therebygenerating a plurality of partial response blocks that are eacha×b_(lag)×d pixels in size, as illustrated in FIG. 21 .

In step S30-5 of FIG. 20 , the response generator module 125-5 generatesan indication of the response of the retina 10 to the light stimulus bycombining the calculated correlations. In the present exampleembodiment, the response generator module 125-5 combines the calculatedcorrelations by performing a matrix addition of the plurality of partialresponse data blocks 600′-1, 600′-2 . . . etc. generated in step S20-5,which are each a×b_(lag)×d pixels in size, to generate a response block(also referred to herein as a “response volume”) 700′, which is athree-dimensional array of combined correlation values that is likewisea×b_(lag)×d array elements in size. The combined correlation values inthe response block 700′ may each be divided by s, to obtain a normalisedresponse.

The three-dimensional array 700′ of combined correlation values mayfurther be processed by the response generator module 125-5, and theresults of those further processing operations may be used by the imagedata generator module 130 to generate image data defining an image whichindicates the response of the retina 10 to the light stimulus fordisplay to a user of the apparatus 100-5, so that an assessment of howwell the retina responds to stimulation can be made. These optionalfurther processing operations will now be described with reference tothe flow diagram in FIG. 22 .

The response volume 700′ may be converted into a two-dimensionalresponse image for easier visualisation by taking the average in thedepth (d) direction, i.e. one value per A-scan per lag time point. Thus,in (optional) step S40-5 of FIG. 22 the response generator module 125-5converts the three-dimensional array 700′ of combined correlationvalues, which is a×b_(lag)×d pixels in size, into a two-dimensionalarray 800′ of correlation values, which is a×b_(lag) pixels in size (asillustrated in FIG. 23(a)), by replacing each one-dimensional array ofcombined correlation values in the three-dimensional array 700′, whichone-dimensional array has been calculated using A-scans that areidentically located in respective B-scans of the sequence 500 ofB-scans, with a single value that is an average of the combinedcorrelation values in the one-dimensional array. The two-dimensionalarray 800′ of combined correlation values indicates the response of theretina 10 to the light stimulus as a function of location along thescanned region R of the retina 10 (i.e. as a function of position alongthe line defining the scan pattern) and time.

The image data generator module 130 may use the two-dimensional array800′ of combined correlation values to generate image data defining animage which indicates the response of the retina 10 to the lightstimulus as a function of location in the scanned region R of the retina10 and time, where the values of a and b_(lag) determine the extent ofthe spatial and temporal variations of the response. However, it may bepreferable to pre-process the two-dimensional array 800′ of combinedcorrelation values generated in step S40-5 prior to image datageneration (or prior to the alternative further processing operationdescribed below), in order to accentuate the time-dependent variabilityof the signal, i.e. the variation of the retinal response to lightstimulation over time. Such pre-processing may be desirable in caseswhere the response variability in the A-scan direction is greater thanin the time lag direction.

The response generator module 125-5 may pre-process the two-dimensionalarray 800′ of combined correlation values, which comprises a sequence ofb_(lag) one-dimensional arrays (A₁, A₂, . . . A_(b) _(lag) ), eachindicating the response of the retina 10 to the light stimulus as afunction of location in the scanned region R of the retina 10, bygenerating a normalised two-dimensional array of combined correlationvalues. The response generator module 125-5 may, as illustrated in FIG.23(b), generate a normalised two-dimensional array, 900′-1, ofcorrelation values by subtracting the first one-dimensional array, A₁,in the sequence of one-dimensional arrays from each remainingone-dimensional array (A₂, A₃, . . . , A_(b) _(lag) ) in the sequence ofone-dimensional arrays. Alternatively, the response generator module125-5 may generate a normalised two-dimensional array of correlationvalues, 900′-2, by calculating an array of averaged combined correlationvalues,

${\overset{\_}{A} = {\frac{1}{b_{lag}}{\sum\limits_{n = 1}^{b_{lag}}A_{n}}}},$such that each averaged combined correlation value in the array ofaveraged combined correlation values is an average (mean) of thecombined correlation values that are correspondingly located in thesequence of one-dimensional arrays, and subtracting the calculated arrayof averaged combined correlation values, Ā, from each of theone-dimensional arrays (A₁, A₂, A₃, . . . , A_(b) _(lag) ) in thesequence of one-dimensional arrays (in other words, performing a vectorsubtraction of the calculated array of averaged correlation values fromeach of the one-dimensional arrays), as illustrated in FIG. 23(c). Inboth of these alternative ways of calculating normalised two-dimensionalarray of combined correlation values, the resulting normalisedtwo-dimensional array of combined correlation values, 900′-1 or 900′-2,indicates the response of the retina 10 to the light stimulus as afunction of location in the scanned region R of the retina 10 and time.

To allow the response of the retina 10 to the light stimulus to beillustrated in a form that may be more useful for a healthcarepractitioner such as an ophthalmologist, the response generator module125-5 may, as shown in step S50-5 of FIG. 22 , convert thetwo-dimensional array of combined correlation values (or the normalisedtwo-dimensional array of combined correlation values, as the case maybe) to a sequence of combined correlation values by replacing each ofthe one-dimensional arrays of combined correlation values in thetwo-dimensional array 800′, 900′-1 or 900′-2 (each of theone-dimensional arrays indicating the response of the retina 10 to thelight stimulus as a function of location in the scanned region R of theretina 10) with a single respective value that is an average of thecombined correlation values in the one-dimensional array, the sequenceof combined correlation values indicating a response of the scannedregion R of the retina 10 to the light stimulus as a function of time.

In step S60 of FIG. 22 , the image data generator module 130 uses thesequence of combined correlation values generated in step S50-5 togenerate image data defining an image which indicates the response ofthe retina 10 to the light stimulus.

The image data may, for example, define an image which indicates thecalculated response of the scanned region R of the retina 10 to thelight stimulus as a function of time; in other words, the strength ofthe correlation of the change in OCT intensity with the time elapsedsince the corresponding stimulus was applied. An example of such animage has been described above with reference to FIG. 7 , and itsdescription will not be repeated here.

Additionally or alternatively, the image data may define an image whichindicates one or more properties of a curve which defines the responseof the scanned region R of the retina 10 to the light stimulus as afunction of time, for example the (solid) response curve shown in FIG. 7. An indicated property of the response curve may (depending on theshape of the curve) be the presence of a change from a predeterminedfirst value to at least a predetermined second (higher or lower) value,the presence of one or more maxima or minima in the response curve, orthe absence of a significant change in the calculated correlationstrength indicated by the response curve (e.g. as determined by thecalculated correlation strength remaining within predefined upper andlower limits), for example. The latter property, i.e. no change in theresponse curve (other than any noise that may be present) might beexpected to be observed in data from diseased eyes, which show little orno response to light stimulation. The indicated property of the responsecurve may alternatively be data (referred to herein as a “marker”) whichquantifies one or more of the aforementioned features of the responsecurve. For example, where there is an extremum (a maximum or a minimum)in the response curve, the image defined by the image data may providean indication of the time to the extremum since the stimulus was appliedand/or an indication of the amplitude of the extremum relative to apredefined reference (e.g. zero correlation strength). Where there is asecond extremum in the response curve (which may be the same or adifferent kind of extremum than the first extremum), the image definedby the image data may additionally or alternatively provide anindication of the time to the second extremum since the stimulus wasapplied and/or an indication of the amplitude of the second extremumrelative to the predefined reference, and/or an indication of thedifference in amplitude between the first and second extrema, forexample. The indication(s) (marker(s)) may be provided in the form ofone or more numerical values, or as a classification of each value intoone of a number of predefined numerical ranges, for example. Eachindication may be augmented, in the image that is defined by the imagedata, with a comment or a colour to indicate whether it is within anormal (healthy) range, or within an abnormal range of values that isindicative of a diseased state.

The image data discussed above represents data that has been aggregatedover the whole of each B-scan, and thus over the whole of the scannedregion R. As a further alternative, respective correlations may becomputed for each of a plurality of different sections of the scannedregion R of the retina (with each section comprising a differentrespective set of A-scans), and these correlations may be mapped to anen-face representation of the retina, either as a diagram or as aretinal image such as a fundus image, a scanning laser ophthalmoscope(SLO) image or an en-face OCT image, for example. In other words, therolling window correlation described above may be calculated separatelyfor each of two or more sections of the sequence of B-scans 500, whichare obtained by dividing each B-scan in the sequence of B-scans 500 inthe same way, into two or more sets of adjacent A-scans, andconcatenating the resulting corresponding sets of A-scans to obtain therespective sections of the sequence of B-scans 500, as illustrated inFIG. 8 (where the B-scans are divided into three equally-sized sectionsin the A-scan direction, by way of an illustrative example, althoughthere may more generally be more or fewer sections, which need not havethe same number of A-scans).

The image data may thus additionally or alternatively define an imagewhich indicates a spatial variation, in the scanned region R of theretina 10, of the one or more properties of the response curve mentionedabove (for example), the spatial variation being overlaid on an en-facerepresentation of at least a portion the retina which includes thescanned region R. The correlations calculated for the different sectionsof the of the scanned region R may be coloured in accordance with anyappropriate colour scheme to indicate at least one the following, forexample: (i) the value of one of the markers in each of the sections;(ii) which of a predefined set of intervals the marker in each of thesections belongs to, based on a reference database, e.g. green for apart of the scanned region of the retina that has provided a signalwhich corresponds to a marker “amplitude of the difference between thefirst and second peak” whose value is within the 95% confidence intervalof a population of healthy eyes; (iii) the percentage of the correlationvalues on the response curve that adheres to the confidence interval ofa reference set of either healthy eyes or eyes with a specific disease;or (iv) aggregate values from the response curve, such as maximum,minimum, mean or median over time, where a darker hue or more red colouris higher than a lighter hue or more blue/green colour, for example.

As described above, FIG. 9 illustrates respective correlation strengthscalculated using the correlation calculation technique of the firstexample embodiment for each of four different sections, R₁, R₂, R₃, andR₄, of the scanned region R of the retina 10 (using four correspondingsections of the sequence of B-scans 500), which are overlaid on arepresentation 1000 of the retina 10. The similar figure may begenerated using the correlation calculation technique of the presentexample embodiment. Where the scan has taken place, different coloursand hues may be used to indicate one of options (i) to (iv) listedabove, for example. In the example of FIG. 9 , the scan pattern on theretina resembles the shape of a figure of 8, although other scanpatterns could alternatively be used.

As with the first example embodiment, the image which indicates theoverlay of the spatial variation (in the scanned region R) of the one ormore properties of the response curve onto an en-face representation maybe turned into an animation by showing how the correlation strengthvaries over time at each scan location in the scanned region R shown inthe image. Colours and hue may be used to represent the amplitude of thecorrelation strength and sign by converting either the absolute strengthor the normalised strength values to different hues, e.g. darker hues toillustrate a stronger signal, and different colours, e.g. blue forpositive correlation and red for negative correlation, for example.

The image data may define an image which is indicative of retinalresponses derived from two separate functional OCT data sets, forexample a first set of functional OCT data that has been acquired froman eye, and a second set of functional OCT data that has subsequentlybeen acquired from the same eye, the image allowing correspondingresponses of the retina to be compared to one another. The image datagenerator 130 may generate image data that allows two main forms ofresults to be displayed, as follows: (i) retinal responses based on thefirst and second sets of functional OCT data, which may be presented inthe same (or same kind of) graph or table in order to enable thehealthcare practitioner to see the absolute values ‘side by side’—thisis applicable to both the correlation strength variations over time(which may, for example, be plotted on a graph) and the derived markers(which may, for example, be presented in columns or rows of a table);and (ii) the difference or a ratio between the retinal responses basedon the first and second sets of functional OCT data. Colour and hue maybe used to show the magnitude and sign (e.g. red for negative and bluefor positive) of the difference, for example. An example of a functionalOCT report defined by such image data is illustrated in FIG. 10 .

It will be appreciated from the foregoing that the fifth exampleembodiment provides another example of a computer-implemented method ofprocessing functional OCT image data, which has been acquired by an OCTimaging device 200 scanning a retina of a subject while the retina isbeing repeatedly stimulated by a light stimulus, to generate image datadefining an image that provides an indication of a response of theretina to the light stimulus. This method comprises receiving, as thefunctional OCT image data: OCT image data that has been generated by theOCT imaging device 200 repeatedly scanning a scanned region of theretina over a time period T; and stimulus data defining a sequence S ofstimulus indicators (s₁, s₂, s₃) each being indicative of a stimulationof the retina by the light stimulus in a respective time interval of asequence of time intervals that spans the time period T. The method alsomakes use of an alternative way of calculating a correlation between asequence of B-scans 500 that is based on the OCT image data and stimulusindicators in the sequence S of stimulus indicators, and uses thecalculated correlation to generate an image which indicates at least oneof: the response of the scanned region of the retina to the lightstimulus as a function of time; one or more properties of a curvedefining the response of the scanned region of the retina to the lightstimulus as a function of time; and a spatial variation, in the scannedregion of the retina, of one or more properties of the curve definingthe response of the scanned region of the retina to the light stimulusas a function of time, the spatial variation being overlaid on anen-face representation of at least a portion the retina which includesthe scanned region.

Embodiment 6

In the fifth example embodiment, the correlation calculator module 120-5is configured to calculate the rolling window correlation between thesequence of B-scans 500 and the sequence S of stimulus indicatorsreceived from the OCT imaging device 200, and the response generatormodule 125-5 is configured to subsequently process the resultingthree-dimensional array 700′ of combined correlation values (in stepS50-5 of FIG. 22 ) so as to generate a two-dimensional array 800′ ofcombined correlation values, by taking the average of the combinedcorrelation values in the depth (d) direction. However, the averagingoperation may, as in the present example embodiment, alternatively beperformed on the B-scans prior to their correlation with the sequence Sof stimulus indicators, thereby simplifying and speeding up thecorrelation calculation.

FIG. 24 is a schematic illustration of an apparatus 100-6 according tothe sixth example embodiment, which comprises, in addition to thereceiver module 110 and the image data generator module 130 that are thesame as those in apparatus 100-5, a B-scan processing module 115 whichis the same as that in the second example embodiment, a responsegenerator module 125-6, and a correlation calculator module 120-6. Theapparatus 100-6 of the present example embodiment thus differs from theapparatus 100-5 of the fifth example embodiment only by comprising theB-scan processing module 115, the response generator module 125-6, andthe correlation calculator module 120-6, whose functionality isexplained in detail below. The following description of the sixthexample embodiment will therefore focus on these differences, with allother details of the fifth example embodiment, which are applicable tothe sixth example embodiment, not being repeated here for sake ofconciseness. It should be noted that the variations and modificationswhich may be made to the fifth example embodiment, as described above,are also applicable to the sixth example embodiment. It should also benoted that one or more of the illustrated components of the apparatus100-6 may be implemented in the form of a programmable signal processinghardware as described above with reference to FIG. 2 , or alternativelyin the form of non-programmable hardware, such as anapplication-specific integrated circuit (ASIC).

FIG. 25 is a flow diagram illustrating a method by which the apparatus100-6 of the sixth example embodiment processes functional OCT data togenerate an indication of a response of the retina 10 to the lightstimulus.

In step S10 of FIG. 25 (which is same as step S10 in FIG. 20 ), thereceiver module 110 receives from the OCT imaging device 200, as thefunctional OCT image data: (i) OCT image data (specifically, in the formof a sequence of B-scans 500) that has been generated by the OCT imagingdevice 200 repeatedly scanning the scanned region R of the retina 10over a time period T; and (ii) stimulus data defining the sequence of sstimulus indicators, each indicative of a stimulation of the retina bythe light stimulus in a respective time interval, T/s, of a sequence oftime intervals that spans the time period T.

In step S15 of FIG. 25 , the B-scan processing module 115 converts thesequence of B-scans 500 received by the receiver module 110 in step S10into a sequence of reduced B-scans 550, by replacing each A-scan in thesequence of A-scans forming each B-scan 400 with a respective averagevalue of A-scan elements of the A-scan, as illustrated in FIG. 13 .

In step S20-6 of FIG. 25 , the correlation calculator module 120-6calculates the rolling window correlation between reduced B-scans in thesequence of reduced B-scans 550 and stimulus indicators s₁, s₂, s₃ . . .in the sequence S of stimulus indicators by calculating, for each of thestimulus indicators, a correlation between stimulus indicators in thewindow comprising the stimulus indicator and the predetermined number ofadjacent stimulus indicators, and reduced B-scans of the sequence ofreduced B-scans 550 that are based on OCT image data generated while theretina 10 was being stimulated in accordance with the stimulusindicators in the window. By way of an example, the correlationcalculator module 120-6 of the present example embodiment calculates,for each of the stimulus indicators, a correlation between stimulusindicators in a windowed portion of the sequence S consisting of astimulus indicator located at a predetermined sequence position in thewindowed portion (e.g. the first sequence indicator in the windowedportion), and a predetermined number of adjacent (e.g. subsequent)stimulus indicators, and corresponding reduced B-scans of the sequenceof reduced B-scans that are based on a portion of the OCT image datagenerated while the retina 10 was being stimulated in accordance withthe stimulus indicators in the window.

In step S30-6 of FIG. 25 , the response generator module 125-6 combinesthe calculated correlations to generate, as the indication of theresponse of the retina 10 to the light stimulus, a two-dimensional arrayof combined correlation values (as shown at 800′ in FIG. 23(a))indicating the response of the retina 10 to the light stimulus as afunction of location in the scanned region R of the retina 10 and time.

The two-dimensional array 800′ of combined correlation values may beprocessed by the image data generator module 130 to generate image datain the same way as in the fifth example embodiment, and/or the responsegenerator module 125-6 may pre-process the two-dimensional array 800′ ofcombined correlation values and/or convert the two-dimensional array ofcombined correlation values (or the normalised two-dimensional array ofcombined correlation values, as the case may be) to a sequence ofcombined correlation values in the same way as the response generatormodule 125-5 of the fifth example embodiment. The sequence of combinedcorrelation values may further be processed by the image data generatormodule 130 to generate image data in the same way as in step S60 of thefifth example embodiment.

Embodiment 7

The processing of functional OCT data that is performed by the apparatus100-5 of the fifth example embodiment allows an indication of thefunctional response of a scanned region R of the retina 10 to beobtained, based on a correlation which is computed for the whole retinaldepth covered by the scan. However, it may be valuable for determiningdisease diagnosis to be able to generate an indication of the individualfunctional responses of one or more retinal layers corresponding todifferent cell types (e.g. photoreceptors, retinal pigment epithelium,retinal nerve fiber layer, etc.). Such enhanced functionality isprovided by the apparatus 100-7 of the seventh example embodiment, whichwill now be described with reference to FIGS. 26 and 27 .

FIG. 26 is a schematic illustration of an apparatus 100-7 for processingfunctional OCT image data to generate an indication of the individualresponses of one or more layers of the retina 10 to the light stimulus,according to the seventh example embodiment. The apparatus 100-7comprises the same receiver module 110 as the first, second, fifth andsixth example embodiments, a B-scan processing module 117 which is thesame as that of the third example embodiment, a correlation calculatormodule 120-7, a response generator module 125-7, and an image generatormodule 130 which is the same as that of the first, second, fifth andsixth example embodiments. It should also be noted that one or more ofthe illustrated components of the apparatus 100-7 may be implemented inthe form of a programmable signal processing hardware as described abovewith reference to FIG. 2 , or alternatively in the form ofnon-programmable hardware, such as an application-specific integratedcircuit (ASIC). Processing operations performed by the apparatus 100-7will now be described with reference to FIG. 27 .

FIG. 27 is a flow diagram illustrating a method by which the apparatus100-7 of the seventh example embodiment processes functional OCT data togenerate an indication of the response of one or more layers of theretina 10 to the light stimulus.

In step S10 of FIG. 27 , the receiver module 110 receives the functionalOCT image data from the OCT imaging device 200. Step S10 in FIG. 27 isthe same as step S10 in FIGS. 3, 12, 15, 18, 20 and 25 , and willtherefore not be described in further detail here.

In step S12 of FIG. 27 , the B-scan processing module 117 identicallysegments each B-scan 400 in the sequence of B-scans 500 into a pluralityof B-scan layers, so that each B-scan layer comprises respectivesections of the A-scans forming the B-scan 400. Step S12 in FIG. 27 isthe same as step S12 in FIG. 15 , and its description will therefore notbe repeated here. The B-scan processing module 117 further concatenatescorresponding B-scan layers from the segmented B-scans to generatesequences of concatenated B-scan layers. Each of the sequences ofconcatenated B-scan layers thus forms a three-dimensional array ofA-scan elements, which corresponds to a respective later of the retina10.

In step S20-7 of FIG. 27 , the correlation calculator module 120-7calculates, for each of at least one sequence of concatenated B-scanlayers of the sequences of concatenated B-scan layers generated in stepS12 of FIG. 27 , a respective rolling window correlation between thesequence of concatenated B-scan layers and the sequence S of stimulusindicators by calculating, for each stimulus indicator (s₁, s₂, s₃) inthe sequence of stimulus indicators, a correlation between stimulusindicators in the window comprising the stimulus indicator and thepredetermined number of adjacent stimulus indicators, and B-scan layersof the B-scan layers that are based on B-scans which have been generatedby the OCT imaging device 100 while the retina 10 was being stimulatedin accordance with the stimulus indicators in the window. In the presentexample embodiment, the correlation calculator module 120-7 thuscalculates, for each of the stimulus indicators, a correlation betweenstimulus indicators in a windowed portion of the sequence S consistingof a stimulus indicator located at a predetermined sequence position inthe windowed portion (e.g. the first sequence indicator in the windowedportion), and a predetermined number of adjacent (e.g. subsequent)stimulus indicators, and corresponding B-scan layers of the sequence ofB-scan layers that are based on a portion of the OCT image datagenerated while the retina 10 was being stimulated in accordance withthe stimulus indicators in the window.

In step S30-7 of FIG. 27 , for each of the at least one sequence ofconcatenated B-scan layers, the response generator module 125-7 combinesthe correlations calculated in step S20-7 to generate a respectivethree-dimensional array of values (“response volume”) that provides anindication of a response of the respective layer of the retina 10 to thelight stimulus.

Each resulting three-dimensional array of combined correlation valuesmay further be processed by the response generator module 125-7, and theresults of those further processing operations may be used by the imagedata generator module 130 to generate image data defining an image whichindicates the response of the corresponding layer of the retina 10 tothe light stimulus for display to a user of the apparatus 100-7, usingthe further processing operations that have been explained in the abovedescription of the first embodiment, with reference to FIG. 5 .

More particularly, the response volume corresponding to each retinallayer may be reduced to a two-dimensional response image for easiervisualisation by taking the average in the depth (d) direction, i.e. onevalue per A-scan per lag time point. Thus, the response generator module125-7 may convert each three-dimensional array of combined correlationvalues, which is a/3×b_(lag)×d pixels in size in the present exampleembodiment, into a respective two-dimensional array of combinedcorrelation values, which is a/3×b_(lag) pixels in size, by replacingeach one-dimensional array of combined correlation values in thethree-dimensional array, which one-dimensional array has been calculatedusing sections of A-scans that are identically located in respectiveB-scans of the sequence of B-scans, with a single value that is anaverage of the combined correlation values in the one-dimensional array.Thus, each array element of the one-dimensional array is calculated onthe basis of a corresponding element of an A-scan. The two-dimensionalarray of combined correlation values indicates the response of thecorresponding layer of the retina 10 to the light stimulus as a functionof location along the scanned region R of the retina 10 (i.e. as afunction of position along the line defining the scan pattern) and time.

The image data generator module 130 may use at least one of thetwo-dimensional arrays of combined correlation values to generate imagedata defining an image which indicates the response, to the lightstimulus, of a respective layer of the retina 10 corresponding to eachof the at least one of the two-dimensional arrays as a function oflocation in the scanned region R of the retina 10 and time. However, itmay be preferable to pre-process at least some of the two-dimensionalarrays of combined correlation values prior to image data generation (orprior to the alternative further processing operation described below),in order to accentuate the time-dependent variability of the signal,i.e. the variation of the retinal layer response to light stimulationover time. Such pre-processing may be desirable in cases where theresponse variability in the A-scan direction is greater than in the timelag direction.

The response generator module 125-7 may pre-process one or more of thetwo-dimensional arrays of combined correlation values, each comprising asequence of b_(lag) one-dimensional arrays, each indicating the responseof the corresponding layer of the retina 10 to the light stimulus as afunction of location in the scanned region R of the retina 10, togenerate a normalised two-dimensional array of combined correlationvalues. The response generator module 125-7 may generate the normalisedtwo-dimensional array of combined correlation values by subtracting thefirst one-dimensional array in the sequence of one-dimensional arraysfrom each remaining one-dimensional array in the sequence ofone-dimensional arrays. Alternatively, the response generator module125-7 may generate a normalised two-dimensional array of combinedcorrelation values by calculating an array of averaged combinedcorrelation values, such that each averaged combined correlation valuein the array of averaged combined correlation values is an average(mean) of the combined correlation values that are correspondinglylocated in the sequence of one-dimensional arrays, and subtracting thecalculated array of averaged combined correlation values from each ofthe one-dimensional arrays in the sequence of one-dimensional arrays (inother words, performing a vector subtraction of the calculated array ofaveraged combined correlation values from each of the one-dimensionalarrays). In both of these alternative ways of calculating normalisedtwo-dimensional array of combined correlation values, the resultingnormalised two-dimensional array of combined correlation valuesindicates the response of the corresponding layer of the retina to thelight stimulus as a function of location in the scanned region R of theretina 10 and time. The image data generator module 130 may use eachnormalised two-dimensional array of combined correlation values togenerate image data defining an image that indicates the response of thecorresponding layer of the retina 10 to the light stimulus as a functionof location in the scanned region R of the retina 10 and time.

To allow the response of one or more layers of the retina to the lightstimulus to be illustrated in a form that may be more useful for ahealthcare practitioner such as an ophthalmologist, the responsegenerator module 125-7 may convert the two-dimensional array of combinedcorrelation values (or the normalised two-dimensional array of combinedcorrelation values, as the case may be) corresponding to each of one ormore of the retinal layers to a sequence of correlation values byreplacing each of the one-dimensional arrays of combined correlationvalues in the two-dimensional array (each of the one-dimensional arraysindicating the response of the corresponding layer of the retina 10 tothe light stimulus as a function of location in the scanned region R ofthe retina 10) with a single respective value that is an average of thecombined correlation values in the one-dimensional array, each sequenceof combined correlation values indicating a response of the respectivelayer of the retina in the scanned region to the light stimulus as afunction of time.

The image data generator module 130 may use one or more of the sequencesof combined correlation values to generate image data defining an imagethat indicates the response of the respective one or more layers of theretina 10 in the scanned region R of the retina 10 to the lightstimulus.

Similar to the fifth and sixth example embodiments described above, theimage data generator module 130 may use one or more sequences ofcombined correlation values to generate an image which indicates atleast one of: the response of the respective one or more layers of theretina 10 in the scanned region R to the light stimulus as a function oftime; one or more properties of a respective one or more curves definingthe response of the respective one or more layers of the retina 10 inthe scanned region R to the light stimulus as a function of time; and aspatial variation, in the scanned region R of the retina 10, of one ormore properties of the respective one or more curves defining theresponse of the respective one or more layers of the retina 10 in thescanned region R to the light stimulus as a function of time, thespatial variation being overlaid on an en-face representation of atleast a portion the retina 10 which includes the scanned region R.

Embodiment 8

In the seventh example embodiment, the correlation calculator module120-7 is, in one configuration, configured to calculate, for each of atleast one sequence of concatenated B-scan layers of the concatenatedsequences of B-scan layers, a respective rolling window correlationbetween the sequence of concatenated B-scan layers and the sequence S ofstimulus indicators received from the OCT imaging device 200, and theresponse generator module 125-7 is configured to subsequently processthe resulting three-dimensional array of correlation values so as togenerate a two-dimensional array of combined correlation values, bytaking an average of the combined correlation values in the depth (d)direction. However, the averaging operation may, as in the presentexample embodiment, alternatively be performed on the one or more of thesequences of concatenated B-scan layers prior to their correlation withthe sequence S of stimulus indicators, thereby simplifying and speedingup the correlation calculation.

FIG. 28 is a schematic illustration of an apparatus 100-8 according tothe eighth example embodiment, which comprises, in addition to thereceiver module 110 and the image data generator module 130 that are thesame as those in apparatus of the foregoing example embodiments, and aB-scan processing module 118 which is the same as in the fourth exampleembodiment, a correlation calculator module 120-8 and a responsegenerator module 125-8 which are described in detail below. It should benoted that one or more of the illustrated components of the apparatus100-8 may be implemented in the form of a programmable signal processinghardware as described above with reference to FIG. 2 , or alternativelyin the form of non-programmable hardware, such as anapplication-specific integrated circuit (ASIC).

FIG. 29 is a flow diagram illustrating a method by which the apparatus100-8 of the eighth example embodiment processes functional OCT data togenerate an indication of a response of the retina 10 to the lightstimulus.

In step S10 of FIG. 29 , the receiver module 110 receives the functionalOCT image data from the OCT imaging device 200. Step S10 in FIG. 29 isthe same as step S10 in FIG. 3 , for example, and will therefore not bedescribed in further detail here.

In step S12 of FIG. 29 , the B-scan processing module 118 identicallysegments each B-scan 400 in the sequence of B-scans 500 into a pluralityof B-scan layers, so that each B-scan layer comprises respectivesections of the A-scans forming the B-scan 400. Step S12 in FIG. 29 isthe same as step S12 in FIG. 15 , for example, and will therefore not bedescribed in further detail here. Each of the sequences of concatenatedB-scan layers forms a three-dimensional array of A-scan elements, whichcorresponds to a respective later of the retina 10.

In step S17 of FIG. 29 , the B-scan processing module 118 converts eachof at least one of the sequences of concatenated B-scan layers into arespective sequence of concatenated reduced B-scan layers, by replacing,for each B-scan layer in each of the at least one sequence ofconcatenated B-scan layers, the sections of the A-scans forming theB-scan layer with corresponding values of an average of A-scan elementsin the sections of the A-scans. For example, in the illustrative exampleof FIG. 16 , the B-scan processing module 118 converts thethree-dimensional array formed by the first sequence of concatenatedB-scan layers, 450 a, into a two-dimensional array, by replacing thefirst column of B-scan layer (or segment) 400-1 a, comprising A-scanelements a1 and a2, with a single value that is an average of a1 and a2,with the remaining columns of B-scan segment 400-1 a, and the otherB-scan segments 400-1 b, 400-1 c, etc. of the first sequence ofconcatenated B-scan layers 450 a being processed in the same way. TheB-scan processing module 118 may likewise process the second sequence ofconcatenated B-scan layers 450 b and/or the third sequence ofconcatenated B-scan layers 450 c in addition to, or alternatively to,the first sequence of concatenated B-scan layers 450 a. Thus, the B-scanprocessing module 118 can convert each of one or more of thethree-dimensional arrays of OCT measurement values shown in the exampleof FIG. 16 , each of which is a/3×b_(lag)×d pixels in size, into arespective two-dimensional array of values, which is a/3×b_(lag) pixelsin size.

In step S20-8 of FIG. 29 , the correlation calculator module 120-8calculates, for each of at least one sequence of concatenated reducedB-scan layers of the sequences of concatenated reduced B-scan layersgenerated in step S17 of FIG. 29 , a respective rolling windowcorrelation between reduced B-scan layers in the sequence ofconcatenated reduced B-scan layers and stimulus indicators (s₁, s₂, s₃)in the sequence S of stimulus indicators, specifically by calculating,for each stimulus indicator in the sequence S of stimulus indicators, acorrelation between stimulus indicators in the window comprising thestimulus indicator and the predetermined number of adjacent stimulusindicators, and values of the averages calculated using B-scan layerscomprised in B-scans that have been generated by the OCT imaging device200 while the retina 10 was being stimulated in accordance with thestimulus indicators in the window.

In step S30-8 of FIG. 29 , the response generator module 125-8generates, for each of the at least one sequence of concatenated reducedB-scan layers, an indication of a response of a layer of the retina 10corresponding to the sequence of concatenated reduced B-scan layers tothe light stimulus, by combining the calculated correlations to generatea two-dimensional array of correlation values indicating the response ofthe layer of the retina to the light stimulus as a function of locationin the scanned region R of the retina 10 and time.

Each resulting two-dimensional array of correlation values may furtherbe processed by the response generator module 125-8 in the same way asthe two-dimensional array(s) of correlation values is/are processed bythe response generator module 125-7 in the seventh example embodimentdescribed above.

Thus, the image data generator module 130 may use at least one of thetwo-dimensional arrays of correlation values to generate image datadefining an image which indicates the response, to the light stimulus,of a respective layer of the retina 10 corresponding to each of the atleast one of the two-dimensional arrays as a function of location in thescanned region R of the retina 10 and time. However, it may bepreferable to pre-process at least some of the two-dimensional arrays ofcorrelation values prior to image data generation (or prior to thealternative further processing operation described below), in order toaccentuate the time-dependent variability of the signal, i.e. thevariation of the retinal layer response to light stimulation over time.Such pre-processing may be desirable in cases where the responsevariability in the A-scan direction is greater than in the time lagdirection.

The response generator module 125-8 may pre-process one or more of thetwo-dimensional arrays of correlation values, each comprising a sequenceof b_(lag) one-dimensional arrays, each array indicating the response ofthe corresponding layer of the retina 10 to the light stimulus as afunction of location in the scanned region R of the retina 10, togenerate a normalised two-dimensional array of correlation values. Theresponse generator module 125-8 may generate a normalisedtwo-dimensional array of correlation values (indicating the response ofthe corresponding layer of the retina 10 to the light stimulus as afunction of location in the scanned region R of the retina 10 and time)using one of the processes described in the third example embodiment,for example. The image data generator module 130 may use each normalisedtwo-dimensional array of correlation values to generate image datadefining an image that indicates the response of the corresponding layerof the retina 10 to the light stimulus as a function of location in thescanned region R of the retina 10 and time.

To allow the response of one or more layers of the retina to the lightstimulus to be illustrated in a form that may be more useful for ahealthcare practitioner such as an ophthalmologist, the responsegenerator module 125-8 may convert the two-dimensional array ofcorrelation values (or the normalised two-dimensional array ofcorrelation values, as the case may be) corresponding to each of one ormore of the retinal layers to a sequence of correlation values byreplacing each of the one-dimensional arrays of correlation values inthe two-dimensional array (each of the one-dimensional arrays indicatingthe response of the corresponding layer of the retina 10 to the lightstimulus as a function of location in the scanned region R of the retina10) with a single respective value that is an average of the correlationvalues in the one-dimensional array, each sequence of correlation valuesindicating a response of the respective layer of the retina in thescanned region to the light stimulus as a function of time.

The image data generator module 130 may use one or more of the sequencesof correlation values to generate image data defining an image thatindicates the response of the respective one or more layers of theretina 10 in the scanned region R of the retina to the light stimulus.

Similar to the third example embodiment described above, the image datagenerator module 130 may use one or more sequences of correlation valuesto generate an image which indicates at least one of: the response ofthe respective one or more layers of the retina 10 in the scanned regionR to the light stimulus as a function of time; one or more properties ofa respective one or more curves defining the response of the respectiveone or more layers of the retina 10 in the scanned region R to the lightstimulus as a function of time; and a spatial variation, in the scannedregion R of the retina 10, of one or more properties of the respectiveone or more curves defining the response of the respective one or morelayers of the retina 10 in the scanned region R to the light stimulus asa function of time, the spatial variation being overlaid on an en-facerepresentation of at least a portion the retina 10 which includes thescanned region R.

The example aspects described herein avoid limitations, specificallyrooted in computer technology, relating to conventional OCT measurementsystems and methods that require large amounts of tomographic data to beacquired during retina light stimulation evaluations, and which requirecorrelation of tomographic data with timing information of applied lightstimuli. Such conventional methods and systems are complex and undulydemanding on computer resources. By virtue of the example aspectsdescribed herein, on the other hand, retina light stimulationevaluations can be performed in a much less complex manner, and in amanner that may require relatively less computer processing and memoryresources than those required by the conventional systems/methods,thereby enabling the evaluations to be performed in a more highlycomputationally- and resource-efficient manner relative to theconventional systems/methods. Also, by virtue of the foregoingcapabilities of the example aspects described herein, which are rootedin computer technology, the example aspects described herein improvecomputers and computer processing/functionality, and also improve thefield(s) of at least image processing, optical coherence tomography(OCT) and data processing, and the processing of functional OCT imagedata.

Some of the embodiments described above are summarised in the followingexamples E1 to E41:

-   E1. An apparatus (100-1; 100-2) configured to process functional OCT    image data, which has been acquired by an OCT imaging device (200)    scanning a retina of a subject while the retina is being repeatedly    stimulated by a light stimulus, to generate an indication (700) of a    response of the retina to the light stimulus, the apparatus (100-1;    100-2) comprising:    -   a receiver module (110) configured to receive, as the functional        OCT image data:        -   OCT image data that has been generated by the OCT imaging            device (200) repeatedly scanning a scanned region (R) of the            retina over a time period (T); and        -   stimulus data defining a sequence (S) of stimulus indicators            (s₁, s₂, s₃) each being indicative of a stimulation of the            retina by the light stimulus in a respective time interval            of a sequence of time intervals that spans the time period            (T); and    -   a correlation calculator module (120-1) configured to calculate        a rolling window correlation between a sequence of B-scans (500)        that is based on the OCT image data and stimulus indicators (s₁,        s₂, s₃) in the sequence (S) of stimulus indicators by:        -   calculating, for each stimulus indicator (s₁; s₂; s₃), a            product of the stimulus indicator (s₁; s₂; s₃) and a            respective windowed portion of the sequence of B-scans (500)            comprising a B-scan (400) which is based on a portion of the            OCT image data generated while the retina was being            stimulated in accordance with the stimulus indicator; and        -   combining the calculated products to generate the indication            (700) of the response of the retina to the light stimulus.-   E2. The apparatus (100-1) according to E1, wherein:    -   the receiver module (110) is configured to receive a sequence of        B-scans (500), which has been generated by the OCT imaging        device (200) repeatedly scanning the scanned region (R) of the        retina (10) over the time period (T), as the OCT image data; and    -   the correlation calculator module (120-1) is configured to        calculate the rolling window correlation between B-scans in the        sequence of B-scans (500) and stimulus indicators (s₁, s₂, s₃)        in the sequence (S) of stimulus indicators by calculating, for        each stimulus indicator (s₁; s₂; s₃), a product of the stimulus        indicator (s₁; s₂; s₃) and a respective windowed portion of the        sequence of B-scans (500) comprising a B-scan (400) which has        been generated by the OCT imaging device (200) while the retina        was being stimulated in accordance with the stimulus indicator        (s₁; s₂; s₃).-   E3. The apparatus (100-1) according to E2, wherein the correlation    calculator module (120-1) is configured to:    -   combine the calculated products to generate a three-dimensional        array (700) of correlation values, the three-dimensional array        (700) of correlation values comprising one-dimensional arrays of        correlation values that have each been calculated using A-scans        that are identically located in respective B-scans (400) of the        sequence of B-scans (500); and    -   convert the three-dimensional array (700) of correlation values        to a two-dimensional array (800) of correlation values by        replacing each of the one-dimensional arrays of correlation        values with a respective single value that is an average of the        correlation values in the one-dimensional array, the        two-dimensional array (800) of correlation values indicating the        response of the retina to the light stimulus as a function of        location along the scanned region (R) of the retina (10) and        time.-   E4. The apparatus (100-2) according to E1, wherein:    -   the receiver module (110) is configured to receive a sequence of        B-scans (500), which has been generated by the OCT imaging        device (200) repeatedly scanning the scanned region (R) of the        retina (10) over the time period (T), as the OCT image data,        each of the B-scans (400) being formed by a sequence of A-scans;    -   the apparatus (100-2) further comprises a B-scan processing        module (115) configured to convert the sequence of B-scans (500)        into a sequence of reduced B-scans (550), by replacing each        A-scan in the sequence of A-scans forming each B-scan with a        respective average value of A-scan elements of the A-scan; and    -   the correlation calculator module (120-2) is configured to:        -   calculate the rolling window correlation between reduced            B-scans in the sequence of reduced B-scans (550) and            stimulus indicators (s₁, s₂, s₃) in the sequence (S) of            stimulus indicators by calculating, for each stimulus            indicator (s₁; s₂; s₃), a product of the stimulus indicator            (s₁; s₂; s₃) and a respective windowed portion of the            sequence of reduced B-scans (550) comprising a reduced            B-scan which is based on a B-scan of the sequence of B-scans            (500) which has been generated by the OCT imaging device            (200) while the retina (10) was being stimulated in            accordance with the stimulus indicator (s₁; s₂; s₃); and        -   combine the calculated products to generate, as the            indication of the response of the retina (10) to the light            stimulus, a two-dimensional array (800) of correlation            values indicating the response of the retina (10) to the            light stimulus as a function of location in the scanned            region (R) of the retina (10) and time.-   E5. The apparatus (100-1; 100-2) according to E3 or E4, wherein    -   the two-dimensional array (800) of correlation values comprises        an array of one-dimensional arrays of correlation values each        indicating the response of the retina (10) to the light stimulus        as a function of location in the scanned region (R) of the        retina (10), and    -   the correlation calculator module (120-1; 120-2) is further        configured to convert the two-dimensional array (800) of        correlation values to a sequence of correlation values by        replacing each of the one-dimensional arrays of correlation        values in the two-dimensional array (800) with a single        respective value that is an average of the correlation values in        the one-dimensional array, the sequence of correlation values        indicating a response of the scanned region (R) of the retina        (10) to the light stimulus as a function of time.-   E6. The apparatus (100-1; 100-2) according to E3 or E4, wherein    -   the two-dimensional array (800) of correlation values comprises        a sequence of one-dimensional arrays each indicating the        response of the retina (10) to the light stimulus as a function        of location in the scanned region (R) of the retina (10), and    -   the correlation calculator module (120-1; 120-2) is further        configured to generate a normalised two-dimensional array        (900-1) of correlation values by subtracting the first        one-dimensional array (A₁) in the sequence of one-dimensional        arrays from each remaining one-dimensional array in the sequence        of one-dimensional arrays, the normalised two-dimensional array        (900-1) of correlation values indicating the response of the        retina to the light stimulus as a function of location in the        scanned region of the retina and time.-   E7. The apparatus (100-1; 100-2) according to E3 or E4, wherein    -   the two-dimensional array (800) of correlation values comprises        an array of one-dimensional arrays each indicating the response        of the retina (10) to the light stimulus as a function of        location in the scanned region (R) of the retina, and    -   the correlation calculator module (120-1; 120-2) is further        configured to generate a normalised two-dimensional array        (900-2) of correlation values by calculating an array of        averaged correlation values such that each averaged correlation        value in the array of averaged correlation values is an average        of the correlation values that are correspondingly located in        the one-dimensional arrays, and subtracting the calculated array        of averaged correlation values from each of the one-dimensional        arrays in the array of one-dimensional arrays, the normalised        two-dimensional array (900-2) of correlation values indicating        the response of the retina (10) to the light stimulus as a        function of location in the scanned region (R) of the retina        (10) and time.-   E8. The apparatus (100-1; 100-2) according to E6 or E7, wherein    -   the normalised two-dimensional array (900-1; 900-2) comprises        one-dimensional arrays of correlation values, each        one-dimensional array of correlation values being indicative of        the response of the retina to the light stimulus as a function        of location in the scanned region of the retina, and    -   the correlation calculator module (120-1; 120-2) is further        configured to convert the normalised two-dimensional array        (900-1; 900-2) of correlation values to a sequence of        correlation values by replacing each of the one-dimensional        arrays of correlation values in the normalised two-dimensional        array (900-1; 900-2) with a respective single value that is an        average of the correlation values in the one-dimensional array,        the sequence of correlation values indicating a response of the        scanned region (R) of the retina (10) to the light stimulus as a        function of time.-   E9. The apparatus (100-1; 100-2) according to E5 or E8, further    comprising:    -   an image data generator module (130) configured to use the        sequence of correlation values to generate image data defining        an image which indicates the response of the scanned region of        the retina to the light stimulus.-   E10. The apparatus (100-1; 100-2) according to E9, wherein the image    data generator module (130) is configured to use the sequence of    correlation values to generate an image which indicates at least one    of:    -   the response of the scanned region (R) of the retina (10) to the        light stimulus as a function of time;    -   one or more properties of a curve defining the response of the        scanned region (R) of the retina (10) to the light stimulus as a        function of time; and    -   a spatial variation, in the scanned region (R) of the retina        (10), of one or more properties of the curve defining the        response of the scanned region (R) of the retina (10) to the        light stimulus as a function of time, the spatial variation        being overlaid on an en-face representation (1000) of at least a        portion the retina (10) which includes the scanned region (R).-   E11. The apparatus (100-3) according to E1, wherein:    -   the receiver module (110) is configured to receive a sequence of        B-scans, which has been generated by the OCT imaging device        (200) repeatedly scanning the scanned region of the retina over        the time period, as the OCT image data;    -   the apparatus (100-3) further comprises a B-scan processing        module (117) configured to segment each B-scan (400) in the        sequence of B-scans (500) into a plurality of B-scan layers        (400-1 a, 400-1 b, 400-1 c) so that each B-scan layer comprises        respective sections of the A-scans forming the B-scan (400), and        concatenate corresponding B-scan layers from the segmented        B-scans to generate sequences of concatenated B-scan layers (450        a, 450 b, 450 c);    -   the correlation calculator module (120-3) is configured to        calculate, for each of at least one sequence of concatenated        B-scan layers of the sequences of concatenated B-scan layers        (450 a, 450 b, 450 c), a respective rolling window correlation        between concatenated B-scan layers in the sequence of        concatenated B-scan layers and stimulus indicators (s₁, s₂, s₃)        in the sequence (S) of stimulus indicators by:    -   calculating, for each stimulus indicator (s₁; s₂; s₃), a product        of the stimulus indicator (s₁; s₂; s₃) and a respective windowed        portion of the sequence of concatenated B-scan layers comprising        a B-scan layer of the B-scan layers which is based on a B-scan        (400) which has been generated by the OCT imaging device (200)        while the retina (10) was being stimulated in accordance with        the stimulus indicator (s₁; s₂; s₃); and        -   combining the calculated products to generate an indication            of a response of a layer of the retina (10) corresponding to            the sequence of concatenated B-scan layers to the light            stimulus.-   E12. The apparatus (100-3) according to E11, wherein the correlation    calculator module (120-3) is configured to:    -   calculate, as the rolling window correlation for each of the at        least one sequence of concatenated B-scan layers, a respective        three-dimensional array of correlation values, each        three-dimensional array of correlation values comprising        one-dimensional arrays of correlation values that have been        calculated using sections of A-scans that are identically        located in respective B-scans of the sequence of B-scans; and    -   convert each of at least one of the three-dimensional arrays of        correlation values to a respective two-dimensional array of        correlation values by replacing each of the one-dimensional        arrays of correlation values in the three-dimensional array with        a respective single value that is an average of the correlation        values in the one-dimensional array, the two-dimensional array        of correlation values indicating the response of the        corresponding layer of the retina to the light stimulus as a        function of location along the scanned region of the retina and        time.-   E13. The apparatus (100-4) according to E1, wherein:    -   the receiver module (110) is configured to receive a sequence of        B-scans, which has been generated by the OCT imaging device        repeatedly scanning the scanned region of the retina over the        time period, as the OCT image data;    -   the apparatus further comprises a B-scan processing module (118)        configured to:        -   segment each B-scan in the sequence of B-scans into a            plurality of B-scan layers so that each B-scan layer            comprises respective sections of the A-scans forming the            B-scan, and concatenating corresponding B-scan layers from            the segmented B-scans to generate sequences of concatenated            B-scan layers; and        -   convert each of at least one sequence of concatenated B-scan            layers of the sequences of concatenated B-scan layers into a            respective sequence of concatenated reduced B-scan layers,            by replacing, for each B-scan layer in each of the at least            one sequence of concatenated B-scan layers, the sections of            the A-scans forming the B-scan layer with corresponding            values of an average of A-scan elements in the sections of            the A-scans; and    -   the correlation calculator module (120-4) is configured to        calculate, for each of the at least one sequence of concatenated        reduced B-scan layers, a respective rolling window correlation        between reduced B-scan layers in the sequence of concatenated        reduced B-scan layers and stimulus indicators in the sequence of        stimulus indicators by:        -   calculating, for each stimulus indicator, a product of the            stimulus indicator and a respective windowed portion of the            sequence of concatenated reduced B-scan layers comprising a            reduced B-scan layer which is based on a B-scan that has            been generated by the OCT imaging device while the retina            was being stimulated in accordance with the stimulus            indicator; and        -   combining the calculated products to generate a            two-dimensional array of correlation values indicating the            response of a layer of the retina corresponding to the            sequence of concatenated reduced B-scan layers to the light            stimulus as a function of location in the scanned region of            the retina and time.-   E14. The apparatus (100-3; 100-4) according to E12 or E13, wherein    the correlation calculator module (120-3; 120-4) is further    configured to convert each of at least one of two-dimensional arrays    of correlation values to a respective sequence of correlation values    by replacing each one-dimensional array of correlation values in the    two-dimensional array, which one-dimensional array indicates the    response of the layer of the retina (10) corresponding to the    two-dimensional array to the light stimulus as a function of    location in the scanned region (R) of the retina (10), with a single    value that is an average of the correlation values in the    one-dimensional array, the sequence of correlation values indicating    a response of the layer of the retina (10) in the scanned region (R)    to the light stimulus as a function of time.-   E15. The apparatus (100-3; 100-4) according to E12 or E13, wherein    -   each two-dimensional array of correlation values comprises a        sequence of one-dimensional arrays each indicating the response        of the respective layer of the retina (10) to the light stimulus        as a function of location in the scanned region (R) of the        retina (10), and    -   the correlation calculator module (120-3; 120-4) is further        configured to process each two-dimensional array of correlation        values to generate a respective normalised two-dimensional array        of correlation values by subtracting the first one-dimensional        array in the sequence of one-dimensional arrays from each        remaining one-dimensional array in the sequence of        one-dimensional arrays, the normalised two-dimensional array of        correlation values indicating the response of the corresponding        layer of the retina (10) to the light stimulus as a function of        location in the scanned region (R) of the retina (10) and time.-   E16. The apparatus (100-3; 100-4) according to E12 or E13, wherein    -   each two-dimensional array of correlation values comprises an        array of one-dimensional arrays each indicating the response of        the respective layer of the retina (10) to the light stimulus as        a function of location in the scanned region (R) of the retina        (10), and    -   the correlation calculator module (120-3; 120-4) is further        configured to process each two-dimensional array of correlation        values to generate a respective normalised two-dimensional array        of correlation values by calculating an array of averaged        correlation values such that each averaged correlation value in        the array of averaged correlation values is an average of the        correlation values that are correspondingly located in the        one-dimensional arrays, and subtracting the calculated array of        averaged correlation values from each of the one-dimensional        arrays in the array of one-dimensional arrays, the normalised        two-dimensional array of correlation values indicating the        response of the corresponding layer of the retina (10) to the        light stimulus as a function of location in the scanned        region (R) of the retina (10) and time.-   E17. The apparatus (100-3; 100-4) according to E15 or E16, wherein    the correlation calculator module (120-3; 120-4) is further    configured to convert each normalised two-dimensional array of    correlation values to a respective sequence of correlation values by    replacing each one-dimensional array of correlation values in the    normalised two-dimensional array, which one-dimensional array    indicates the response of the layer of the retina corresponding to    the normalised two-dimensional array of correlation values to the    light stimulus as a function of location in the scanned region of    the retina, with a single value that is an average of the    correlation values in the one-dimensional array, the sequence of    correlation values indicating a response of the layer of the retina    (10) in the scanned region (R) to the light stimulus as a function    of time.-   E18. The apparatus (100-3; 100-4) according to E14 or E17, further    comprising:    -   an image data generator module (130) configured to use one or        more of the sequences of correlation values to generate image        data defining an image that indicates the response of the        respective one or more of layers of the retina (10) in the        scanned region (R) of the retina (10) to the light stimulus.-   E19. The apparatus (100-3; 100-4) according to E18, wherein the    image data generator module (130) is configured to use the one or    more sequences of correlation values to generate an image which    indicates at least one of:    -   the response of the respective one or more layers of the retina        (10) in the scanned region (R) to the light stimulus as a        function of time;    -   one or more properties of a respective one or more curves        defining the response of the respective one or more layers of        the retina (10) in the scanned region (R) to the light stimulus        as a function of time; and    -   a spatial variation, in the scanned region of the retina (10),        of one or more properties of the respective one or more curves        defining the response of the respective one or more layers of        the retina (10) in the scanned region (R) to the light stimulus        as a function of time, the spatial variation being overlaid on        an en-face representation of at least a portion the retina (10)        which includes the scanned region (R).-   E20. An apparatus (100-5) configured to process functional OCT image    data, which has been acquired by an OCT imaging device (200)    scanning a retina (10) of a subject while the retina (10) is being    repeatedly stimulated by a light stimulus, to generate an indication    of a response of the retina to the light stimulus, the apparatus    (100-5) comprising:    -   a receiver module (110) configured to receive, as the functional        OCT image data:        -   OCT image data that has been generated by the OCT imaging            device (200) repeatedly scanning a scanned region (R) of the            retina (10) over a time period (T); and        -   stimulus data defining a sequence (S) of stimulus indicators            (s₁, s₂, s₃) each being indicative of a stimulation of the            retina (10) by the light stimulus in a respective time            interval of a sequence of time intervals that spans the time            period (T);    -   a correlation calculator module (120-5) configured to calculate        a rolling window correlation between a sequence of B-scans (500)        that is based on the OCT image data and at least some of the        stimulus indicators (s₁, s₂, s₃) in the sequence (S) of stimulus        indicators by calculating, for each stimulus indicator, a        correlation between        -   stimulus indicators in a window comprising the stimulus            indicator and a predetermined number of adjacent stimulus            indicators, and        -   B-scans of the sequence of B-scans (500) that are based on a            portion of the OCT image data generated while the retina            (10) was being stimulated in accordance with the stimulus            indicators in the window; and    -   a response generator module (125) configured to generate the        indication of the response of the retina (10) to the light        stimulus by combining the calculated correlations.-   E21. The apparatus (100-5) according to E20, wherein:    -   the receiver module (110) is configured to receive a sequence of        B-scans, which has been generated by the OCT imaging device        (200) repeatedly scanning the scanned region (R) of the retina        (10) over the time period, as the OCT image data;    -   the correlation calculator module (120-5) is configured to        calculate the rolling window correlation between the sequence of        B-scans (500) and the sequence (S) of stimulus indicators by        calculating, for each stimulus indicator (s₁, s₂, s₃) in the        sequence (S) of stimulus indicators, a correlation between        -   stimulus indicators in the window comprising the stimulus            indicator and the predetermined number of adjacent stimulus            indicators, and        -   B-scans of the sequence of B-scans (500) that have been            generated by the OCT imaging device (200) while the retina            (10) was being stimulated in accordance with the stimulus            indicators in the window.-   E22. The apparatus (100-5) according to E21, wherein the response    generator module (125) is configured to combine the calculated    correlations to generate a three-dimensional array of combined    correlation values, the three-dimensional array of combined    correlation values comprising one-dimensional arrays of combined    correlation values that have each been calculated using A-scans that    are identically located in respective B-scans of the sequence of    B-scans (500), the response generator module (125) being configured    to generate the indication of the response of the retina (10) to the    light stimulus by:    -   converting the three-dimensional array of combined correlation        values to a two-dimensional array of combined correlation values        by replacing each of the one-dimensional arrays of combined        correlation values with a respective single value that is an        average of the combined correlation values in the        one-dimensional array, the two-dimensional array of combined        correlation values indicating the response of the retina (10) to        the light stimulus as a function of location along the scanned        region (R) of the retina (10) and time.-   E23. The apparatus (100-6) according to E20, wherein:    -   the receiver module (110) is configured to receive a sequence of        B-scans, which has been generated by the OCT imaging device        (200) repeatedly scanning the scanned region (R) of the retina        (10) over the time period (T), as the OCT image data, each of        the B-scans being formed by a sequence of A-scans;    -   the apparatus (100-6) further comprises a B-scan processing        module (115) configured to convert the sequence of B-scans into        a sequence of reduced B-scans, by replacing each A-scan in the        sequence of A-scans forming each B-scan with a respective        average value of A-scan elements of the A-scan;    -   the correlation calculator module (120-6) is configured to        calculate the rolling window correlation between the sequence of        reduced B-scans and the sequence of stimulus indicators by        calculating, for each stimulus indicator (s₁, s₂, s₃) in the        sequence (S) of stimulus indicators, a correlation between        -   stimulus indicators in the window comprising the stimulus            indicator and the predetermined number of adjacent stimulus            indicators, and        -   reduced B-scans of the sequence of reduced B-scans that are            based on OCT image data generated while the retina (10) was            being stimulated in accordance with the stimulus indicators            in the window; and    -   the indication of the response of the retina (10) to the light        stimulus generated by the response generator module (125-6)        comprises a two-dimensional array of combined correlation values        indicating the response of the retina (10) to the light stimulus        as a function of location in the scanned region (R) of the        retina (10) and time.-   E24. The apparatus (100-5; 100-6) according to E22 or E23, wherein    -   the two-dimensional array of combined correlation values        comprises an array of one-dimensional arrays of combined        correlation values each indicating the response of the retina        (10) to the light stimulus as a function of location in the        scanned region (R) of the retina (10), and    -   the response generator module (125-5; 125-6) is configured to        generate the indication of the response of the retina (10) to        the light stimulus by:    -   converting the two-dimensional array of combined correlation        values to a sequence of combined correlation values by replacing        each of the one-dimensional arrays of combined correlation        values in the two-dimensional array with a single respective        value that is an average of the combined correlation values in        the one-dimensional array, the sequence of combined correlation        values indicating a response of the scanned region (R) of the        retina (10) to the light stimulus as a function of time.-   E25. The apparatus (100-5; 100-6) according to E22 or E23, wherein    the two-dimensional array of combined correlation values comprises a    sequence of one-dimensional arrays each indicating the response of    the retina (10) to the light stimulus as a function of location in    the scanned region (R) of the retina (10), and wherein the response    generator module (125-5; 125-6) is configured to generate the    indication of the response of the retina (10) to the light stimulus    further by:    -   generating a normalised two-dimensional array of combined        correlation values by subtracting the first one-dimensional        array in the sequence of one-dimensional arrays from each        remaining one-dimensional array in the sequence of        one-dimensional arrays, the normalised two-dimensional array of        combined correlation values indicating the response of the        retina (10) to the light stimulus as a function of location in        the scanned region (R) of the retina (10) and time.-   E26. The apparatus (100-5; 100-6) according to E22 or E23, wherein    the two-dimensional array of combined correlation values comprises    an array of one-dimensional arrays each indicating the response of    the retina (10) to the light stimulus as a function of location in    the scanned region (R) of the retina (10), and wherein the response    generator module (125-5; 125-6) is configured to generate the    indication of the response of the retina (10) to the light stimulus    by:    -   generating a normalised two-dimensional array of combined        correlation values by calculating an array of averaged combined        correlation values such that each averaged combined correlation        value in the array of averaged combined correlation values is an        average of the combined correlation values that are        correspondingly located in the one-dimensional arrays, and        subtracting the calculated array of averaged combined        correlation values from each of the one-dimensional arrays in        the array of one-dimensional arrays, the normalised        two-dimensional array of combined correlation values indicating        the response of the retina (10) to the light stimulus as a        function of location in the scanned region (R) of the retina        (10) and time.-   E27. The apparatus (100-5; 100-6) according to E25 or E26, wherein    -   the normalised two-dimensional array comprises one-dimensional        arrays of combined correlation values, each one-dimensional        array of combined correlation values being indicative of the        response of the retina to the light stimulus as a function of        location in the scanned region (R) of the retina (10), and    -   the response generator module (125-5; 125-6) is configured to        generate the indication of the response of the retina (10) to        the light stimulus by:    -   converting the normalised two-dimensional array of combined        correlation values to a sequence of combined correlation values        by replacing each of the one-dimensional arrays of combined        correlation values in the normalised two-dimensional array with        a respective single value that is an average of the combined        correlation values in the one-dimensional array, the sequence of        combined correlation values indicating a response of the scanned        region (R) of the retina (10) to the light stimulus as a        function of time.-   E28. The apparatus (100-5; 100-6) according to E24 or E27, further    comprising:    -   an image data generator module (130) configured to use the        sequence of combined correlation values to generate image data        defining an image which indicates the response of the scanned        region (R) of the retina (10) to the light stimulus as a        function of time.-   E29. The apparatus (100-5; 100-6) according to E28, wherein the    image data generator module (130) is configured to use the sequence    of correlation values to generate an image which indicates at least    one of:    -   the response of the scanned region (R) of the retina (10) to the        light stimulus as a function of time;    -   one or more properties of a curve defining the response of the        scanned region (R) of the retina (10) to the light stimulus as a        function of time; and    -   a spatial variation, in the scanned region (R) of the retina        (10), of one or more properties of the curve defining the        response of the scanned region (R) of the retina (10) to the        light stimulus as a function of time, the spatial variation        being overlaid on an en-face representation (1000) of at least a        portion the retina (10) which includes the scanned region (R).-   E30. The apparatus (100-7) according to E20, wherein:    -   the receiver module (110) is configured to receive a sequence of        B-scans, which has been generated by the OCT imaging device        (200) repeatedly scanning the scanned region (R) of the retina        (10) over the time period, as the OCT image data;    -   the apparatus further comprises a B-scan processing module (117)        configured o segment each B-scan in the sequence of B-scans        (500) into a plurality of B-scan layers so that each B-scan        layer comprises respective sections of the A-scans forming the        B-scan, and concatenate corresponding B-scan layers from the        segmented B-scans to generate sequences of concatenated B-scan        layers;    -   the correlation calculator module (120-7) is configured to        calculate, for each of at least one sequence of concatenated        B-scan layers of the sequences of concatenated B-scan layers, a        respective rolling window correlation between the sequence of        concatenated B-scan layers and the sequence of stimulus        indicators by calculating, for each stimulus indicator in the        sequence of stimulus indicators, a correlation between        -   stimulus indicators in the window comprising the stimulus            indicator and the predetermined number of adjacent stimulus            indicators, and        -   B-scan layers of the B-scan layers that are based on B-scans            which have been generated by the OCT imaging device (200)            while the retina (10) was being stimulated in accordance            with the stimulus indicators in the window; and    -   the response generator module (125-7) is configured to generate        the indication of the response of the retina (10) to the light        stimulus by generating, for each of the at least one sequence of        concatenated B-scan layers, an indication of a response of a        layer of the retina (10) corresponding to the sequence of        concatenated B-scan layers to the light stimulus, by combining        the calculated correlations.-   E31. The apparatus (100-7) according to E30, wherein    -   the correlation calculator module (120-7) is configured to        calculate, as the rolling window correlation for each of the at        least one sequence of concatenated B-scan layers, a respective        three-dimensional array of combined correlation values, each        three-dimensional array of combined correlation values        comprising one-dimensional arrays that have been calculated        using sections of A-scans that are identically located in        respective B-scans of the sequence of B-scans, and    -   the response generator module (125-7) is configured to generate        the indication of the response to the light stimulus of a        respective layer of the retina (10) corresponding to each of the        at least one sequence of concatenated B-scan layers by:    -   converting the three-dimensional array of combined correlation        values to a two-dimensional array of combined correlation values        by replacing each of the one-dimensional arrays of combined        correlation values in the three-dimensional array with a        respective single value that is an average of the combined        correlation values in the one-dimensional array, the        two-dimensional array of combined correlation values indicating        the response of the retina (10) to the light stimulus as a        function of location along the scanned region (R) of the retina        (10) and time.-   E32. The apparatus (100-8) according to E20, wherein:    -   the receiver module (110) is configured to receive a sequence of        B-scans, which has been generated by the OCT imaging device        (200) repeatedly scanning the scanned region (R) of the retina        (10) over the time period, as the OCT image data;    -   the apparatus (100-8) further comprises a B-scan processing        module (118) configured to:        -   segment each B-scan in the sequence of B-scans (500) into a            plurality of B-scan layers so that each B-scan layer            comprises respective sections of the A-scans forming the            B-scan, and concatenate corresponding B-scan layers from the            segmented B-scans to generate sequences of concatenated            B-scan layers; and        -   convert each of at least one sequence of concatenated B-scan            layers of the sequences of concatenated B-scan layers into a            respective sequence of concatenated reduced B-scan layers,            by replacing, for each B-scan layer in each of the at least            one sequence of concatenated B-scan layers, the sections of            the A-scans forming the B-scan layer with corresponding            values of an average of A-scan elements in the sections of            the A-scans;    -   the correlation calculator module (120-8) is configured to        calculate, for each of the at least one sequence of concatenated        reduced B-scan layers, a respective rolling window correlation        between the sequence of concatenated reduced B-scan layers and        the sequence of stimulus indicators by calculating, for each        stimulus indicator in the sequence of stimulus indicators, a        correlation between        -   stimulus indicators in the window comprising the stimulus            indicator and the predetermined number of adjacent stimulus            indicators, and        -   values of the averages calculated using B-scan layers            comprised in B-scans that have been generated by the OCT            imaging device (200) while the retina (10) was being            stimulated in accordance with the stimulus indicators in the            window; and    -   the response generator module (125-8) is configured to generate        the indication of the response of the retina (10) to the light        stimulus by generating, for each of the at least one sequence of        concatenated reduced B-scan layers, an indication of a response        of a layer of the retina corresponding to the sequence of        concatenated reduced B-scan layers to the light stimulus, by        combining the calculated correlations to generate a        two-dimensional array of combined correlation values indicating        the response of the layer of the retina (10) to the light        stimulus as a function of location in the scanned region (R) of        the retina (10) and time.-   E33. The apparatus (100-7; 100-8) according to E31 or E32, wherein    -   the response generator module (125-7; 125-8) is configured to        generate the indication of the response to the light stimulus of        each layer of the retina (10) corresponding to the at least one        sequence of concatenated reduced B-scan layers by:    -   converting the respective two-dimensional array of combined        correlation values to a respective sequence of combined        correlation values by replacing each one-dimensional array of        combined correlation values in the two-dimensional array, which        one-dimensional array indicates the response of the layer of the        retina (10) to the light stimulus as a function of location in        the scanned region (r) of the retina (10), with a single value        that is an average of the combined correlation values in the        one-dimensional array, the sequence of combined correlation        values indicating a response of the layer of the retina (10) in        the scanned region (R) to the light stimulus as a function of        time.-   E34. The apparatus (100-7; 100-8) according to E31 or E32, wherein    each two-dimensional array of combined correlation values comprises    a sequence of one-dimensional arrays each indicating the response of    the respective layer of the retina (10) to the light stimulus as a    function of location in the scanned region (R) of the retina (10),    and wherein the response generator module (125-7; 125-8) is    configured to generate the indication of the response to the light    stimulus of each layer of the retina (10) corresponding to the    respective one of the at least one sequence of concatenated B-scan    layers by:    -   generating a normalised two-dimensional array of combined        correlation values by subtracting the first one-dimensional        array in the sequence of one-dimensional arrays from each        remaining one-dimensional array in the sequence of        one-dimensional arrays, the normalised two-dimensional array of        combined correlation values indicating the response of the layer        of the retina (10) to the light stimulus as a function of        location in the scanned region (R) of the retina (10) and time.-   E35. The apparatus (100-7; 100-8) according to E31 or E32, wherein    each two-dimensional array of combined correlation values comprises    an array of one-dimensional arrays each indicating the response of    the respective layer of the retina (10) to the light stimulus as a    function of location in the scanned region (R) of the retina (10),    and wherein the response generator module (125-7; 125-8) is    configured to generate the indication of the response to the light    stimulus of each layer of the retina (10) corresponding to the    respective one of the at least one sequence of concatenated B-scan    layers by:    -   generating a normalised two-dimensional array of combined        correlation values by calculating an array of averaged combined        correlation values such that each averaged combined correlation        value in the array of averaged combined correlation values is an        average of the combined correlation values that are        correspondingly located in the one-dimensional arrays, and        subtracting the calculated array of averaged combined        correlation values from each of the one-dimensional arrays in        the array of one-dimensional arrays, the normalised        two-dimensional array of combined correlation values indicating        the response of the layer of the retina (10) to the light        stimulus as a function of location in the scanned region (R) of        the retina (10) and time.-   E36. The apparatus (100-7; 100-8) according to E34 or E35, wherein    the response generator module (125-7; 125-8) is configured to    generate the indication of the response to the light stimulus of    each layer of the retina (10) corresponding to the at least one    sequence of concatenated reduced B-scan layers by:    -   converting the respective normalised two-dimensional array of        combined correlation values to a respective sequence of combined        correlation values by replacing each one-dimensional array of        combined correlation values in the normalised two-dimensional        array, which one-dimensional array indicates the response of the        layer of the retina to the light stimulus as a function of        location in the scanned region of the retina, with a single        value that is an average of the combined correlation values in        the one-dimensional array, the sequence of combined correlation        values indicating a response of the layer of the retina (10) in        the scanned region (R) to the light stimulus as a function of        time.-   E37. The apparatus (100-7; 100-8) according to E33 or E36, further    comprising:    -   an image data generator module (130) configured to use the        sequence of combined correlation values to generate image data        defining an image that indicates the response of the layer of        the retina (10) in the scanned region (R) of the retina (10) to        the light stimulus as a function of time.-   E38. The apparatus (100-7; 100-8) according to E37, wherein the    image data generator module (130) is configured to use the one or    more sequences of correlation values to generate an image which    indicates at least one of:    -   the response of the respective one or more layers of the retina        (10) in the scanned region (R) to the light stimulus as a        function of time;    -   one or more properties of a respective one or more curves        defining the response of the respective one or more layers of        the retina (10) in the scanned region (R) to the light stimulus        as a function of time; and    -   a spatial variation, in the scanned region (R) of the retina        (10), of one or more properties of the respective one or more        curves defining the response of the respective one or more        layers of the retina (10) in the scanned region (R) to the light        stimulus as a function of time, the spatial variation being        overlaid on an en-face representation of at least a portion the        retina (10) which includes the scanned region (R).-   E39. The apparatus (100-1 to 100-8) according to any of E1 to E38,    wherein the light stimulus comprises a light stimulus providing    illumination over a whole visual field of the subject.-   E40. The apparatus (100-1 to 100-8) according to any of E1 to E39,    wherein the sequence of stimulus indicators indicates a random or    pseudo-random stimulation of the retina (10) over time.-   E41. The apparatus (100-1 to 100-8) according to any of E1 to E40,    wherein each stimulus indicator in the sequence of stimulus    indicators is indicative of whether or not the retina (10) was    stimulated by the light stimulus, or a change in stimulation of the    retina (10) by the light stimulus, in a respective time interval of    the sequence of time intervals that spans the time period (T).

In the foregoing description, example aspects are described withreference to several example embodiments. Accordingly, the specificationshould be regarded as illustrative, rather than restrictive. Similarly,the figures illustrated in the drawings, which highlight thefunctionality and advantages of the example embodiments, are presentedfor example purposes only. The architecture of the example embodimentsis sufficiently flexible and configurable, such that it may be utilized(and navigated) in ways other than those shown in the accompanyingfigures.

Software embodiments of the examples presented herein may be provided asa computer program, or software, such as one or more programs havinginstructions or sequences of instructions, included or stored in anarticle of manufacture such as a machine-accessible or machine-readablemedium, an instruction store, or computer-readable storage device, eachof which can be non-transitory, in one example embodiment. The programor instructions on the non-transitory machine-accessible medium,machine-readable medium, instruction store, or computer-readable storagedevice, may be used to program a computer system or other electronicdevice. The machine- or computer-readable medium, instruction store, andstorage device may include, but are not limited to, floppy diskettes,optical disks, and magneto-optical disks or other types ofmedia/machine-readable medium/instruction store/storage device suitablefor storing or transmitting electronic instructions. The techniquesdescribed herein are not limited to any particular softwareconfiguration. They may find applicability in any computing orprocessing environment. The terms “computer-readable”,“machine-accessible medium”, “machine-readable medium”, “instructionstore”, and “computer-readable storage device” used herein shall includeany medium that is capable of storing, encoding, or transmittinginstructions or a sequence of instructions for execution by the machine,computer, or computer processor and that causes themachine/computer/computer processor to perform any one of the methodsdescribed herein. Furthermore, it is common in the art to speak ofsoftware, in one form or another (e.g. program, procedure, process,application, module, unit, logic, and so on), as taking an action orcausing a result. Such expressions are merely a shorthand way of statingthat the execution of the software by a processing system causes theprocessor to perform an action to produce a result.

Some embodiments may also be implemented by the preparation ofapplication-specific integrated circuits, field-programmable gatearrays, or by interconnecting an appropriate network of conventionalcomponent circuits.

Some embodiments include a computer program product. The computerprogram product may be a storage medium or media, instruction store(s),or storage device(s), having instructions stored thereon or thereinwhich can be used to control, or cause, a computer or computer processorto perform any of the procedures of the example embodiments describedherein. The storage medium/instruction store/storage device may include,by example and without limitation, an optical disc, a ROM, a RAM, anEPROM, an EEPROM, a DRAM, a VRAM, a flash memory, a flash card, amagnetic card, an optical card, nanosystems, a molecular memoryintegrated circuit, a RAID, remote data storage/archive/warehousing,and/or any other type of device suitable for storing instructions and/ordata.

Stored on any one of the computer-readable medium or media, instructionstore(s), or storage device(s), some implementations include softwarefor controlling both the hardware of the system and for enabling thesystem or microprocessor to interact with a human user or othermechanism utilizing the results of the example embodiments describedherein. Such software may include without limitation device drivers,operating systems, and user applications. Ultimately, suchcomputer-readable media or storage device(s) further include softwarefor performing example aspects herein, as described above.

Included in the programming and/or software of the system are softwaremodules for implementing the procedures described herein. In someexample embodiments herein, a module includes software, although inother example embodiments herein, a module includes hardware, or acombination of hardware and software.

While various example embodiments have been described above, it shouldbe understood that they have been presented by way of example, and notlimitation. It will be apparent to persons skilled in the relevantart(s) that various changes in form and detail can be made therein.Thus, the present invention should not be limited by any of the abovedescribed example embodiments, but should be defined only in accordancewith the following claims and their equivalents.

Further, the purpose of the Abstract is to enable the Patent Office andthe public generally, and especially the scientists, engineers andpractitioners in the art who are not familiar with patent or legal termsor phraseology, to determine quickly from a cursory inspection thenature and essence of the technical disclosure of the application. TheAbstract is not intended to be limiting as to the scope of the exampleembodiments presented herein in any way. It is also to be understoodthat the procedures recited in the claims need not be performed in theorder presented.

While this specification contains many specific embodiment details,these should not be construed as limiting, but rather as descriptions offeatures specific to particular embodiments described herein. Certainfeatures that are described in this specification in the context ofseparate embodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable sub-combination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asub-combination or variation of a sub-combination.

In certain circumstances, multitasking and parallel processing may beadvantageous. Moreover, the separation of various components in theembodiments described above should not be understood as requiring suchseparation in all embodiments, and it should be understood that thedescribed program components and systems can generally be integratedtogether in a single software product or packaged into multiple softwareproducts.

Having now described some illustrative embodiments and embodiments, itis apparent that the foregoing is illustrative and not limiting, havingbeen presented by way of example. In particular, although many of theexamples presented herein involve specific combinations of apparatus orsoftware elements, those elements may be combined in other ways toaccomplish the same objectives. Acts, elements and features discussedonly in connection with one embodiment are not intended to be excludedfrom a similar role in other embodiments or embodiments.

The apparatus and computer programs described herein may be embodied inother specific forms without departing from the characteristics thereof.The foregoing embodiments are illustrative rather than limiting of thedescribed systems and methods.

Scope of the apparatus and computer programs described herein is thusindicated by the appended claims, rather than the foregoing description,and changes that come within the meaning and range of equivalency of theclaims are embraced therein.

The invention claimed is:
 1. An apparatus configured to processfunctional OCT image data, which has been acquired by an OCT imagingdevice (200) scanning a retina of a subject while the retina is beingrepeatedly stimulated by a light stimulus, to generate an indication ofa response of the retina to the light stimulus, the apparatuscomprising: a receiver module configured to receive, as the functionalOCT image data: OCT image data that has been generated by the OCTimaging device repeatedly scanning a scanned region (R) of the retinaover a time period; and stimulus data defining a sequence of stimulusindicators each being indicative of a stimulation of the retina by thelight stimulus in a respective time interval of a sequence of timeintervals that spans the time period; and a correlation calculatormodule configured to calculate a rolling window correlation between asequence of B-scans that is based on the OCT image data and stimulusindicators in the sequence of stimulus indicators.
 2. The apparatusaccording to claim 1, wherein the correlation calculator module isconfigured to calculate the rolling window correlation between thesequence of B-scans and stimulus indicators in the sequence of stimulusindicators by: calculating, for each stimulus indicator, a product ofthe stimulus indicator and a respective windowed portion of the sequenceof B-scans comprising a B-scan which is based on a portion of the OCTimage data generated while the retina was being stimulated in accordancewith the stimulus indicator; and combining the calculated products togenerate the indication of the response of the retina to the lightstimulus.
 3. The apparatus according to claim 2, wherein: the receivermodule is configured to receive a sequence of B-scans, which has beengenerated by the OCT imaging device repeatedly scanning the scannedregion of the retina over the time period, as the OCT image data; andthe correlation calculator module is configured to calculate the rollingwindow correlation between B-scans in the sequence of B-scans andstimulus indicators in the sequence of stimulus indicators bycalculating, for each stimulus indicator, a product of the stimulusindicator and a respective windowed portion of the sequence of B-scanscomprising a B-scan which has been generated by the OCT imaging devicewhile the retina was being stimulated in accordance with the stimulusindicator.
 4. The apparatus according to claim 3, wherein thecorrelation calculator module is configured to: combine the calculatedproducts to generate a three-dimensional array of correlation values,the three-dimensional array of correlation values comprisingone-dimensional arrays of correlation values that have each beencalculated using A-scans that are identically located in respectiveB-scans of the sequence of B-scans; and convert the three-dimensionalarray of correlation values to a two-dimensional array of correlationvalues by replacing each of the one-dimensional arrays of correlationvalues with a respective single value that is an average of thecorrelation values in the one-dimensional array, the two-dimensionalarray of correlation values indicating the response of the retina to thelight stimulus as a function of location along the scanned region of theretina and time.
 5. The apparatus according to claim 1, wherein thecorrelation calculator module is configured to calculate the rollingwindow correlation between the sequence of B-scans and stimulusindicators in the sequence of stimulus indicators by calculating, foreach stimulus indicator, a correlation between stimulus indicators in awindow comprising the stimulus indicator and a predetermined number ofadjacent stimulus indicators, and B-scans of the sequence of B-scansthat are based on a portion of the OCT image data generated while theretina was being stimulated in accordance with the stimulus indicatorsin the window, and the apparatus further comprises a response generatormodule configured to generate the indication of the response of theretina to the light stimulus by combining the calculated correlations.6. The apparatus according to claim 5, wherein: the receiver module isconfigured to receive a sequence of B-scans, which has been generated bythe OCT imaging device repeatedly scanning the scanned region of theretina over the time period, as the OCT image data; the correlationcalculator module is configured to calculate the rolling windowcorrelation between the sequence of B-scans and the sequence of stimulusindicators by calculating, for each stimulus indicator in the sequenceof stimulus indicators, a correlation between stimulus indicators in thewindow comprising the stimulus indicator and the predetermined number 5of adjacent stimulus indicators, and B-scans of the sequence of B-scansthat have been generated by the OCT imaging device while the retina wasbeing stimulated in accordance with the stimulus indicators in thewindow.
 7. The apparatus according to claim 6, wherein the responsegenerator module is configured to combine the calculated correlations togenerate a three-dimensional array of combined correlation values, thethree-dimensional array of combined correlation values comprisingone-dimensional arrays of combined correlation values that have eachbeen calculated using A-scans that are identically located in respectiveB-scans of the sequence of B-scans, the response generator module beingconfigured to generate the indication of the response of the retina tothe light stimulus by: converting the three-dimensional array ofcombined correlation values to a two-dimensional array of combinedcorrelation values by replacing each of the one-dimensional arrays ofcombined correlation values with a respective single value that is anaverage of the combined correlation values in the one-dimensional array,the two-dimensional array of combined correlation values indicating theresponse of the retina to the light stimulus as a function of locationalong the scanned region of the retina and time.
 8. The apparatusaccording to claim 2, wherein: the receiver module is configured toreceive a sequence of B-scans, which has been generated by the OCTimaging device repeatedly scanning the scanned region of the retina overthe time period, as the OCT image data, each of the B-scans being formedby a sequence of A-scans; the apparatus further comprises a B-scanprocessing module configured to convert the sequence of B-scans into asequence of reduced B-scans, by replacing each A-scan in the sequence ofA-scans forming each B-scan with a respective average value of A-scanelements of the A-scan; and the correlation calculator module isconfigured to: calculate the rolling window correlation between reducedB-scans in the sequence of reduced B-scans and stimulus indicators inthe sequence of stimulus indicators by calculating, for each stimulusindicator, a product of the stimulus indicator and a respective windowedportion of the sequence of reduced B-scans comprising a reduced B-scanwhich is based on a B-scan of the sequence of B-scans which has beengenerated by the OCT imaging device while the retina was beingstimulated in accordance with the stimulus indicator; and combine thecalculated products to generate, as the indication of the response ofthe retina to the light stimulus, a two-dimensional array of correlationvalues indicating the response of the retina to the light stimulus as afunction of location in the scanned region of the retina and time. 9.The apparatus according to claim 5, wherein: the receiver module isconfigured to receive a sequence of B-scans, which has been generated bythe OCT imaging device repeatedly scanning the scanned region of theretina over the time period, as the OCT image data, each of the B-scansbeing formed by a sequence of A-scans; the apparatus further comprises aB-scan processing module configured to convert the sequence of B-scansinto a sequence of reduced B-scans, by replacing each A-scan in thesequence of A-scans forming each B-scan with a respective average valueof A-scan elements of the A-scan; the correlation calculator module isconfigured to calculate the rolling window correlation between thesequence of reduced B-scans and the sequence of stimulus indicators bycalculating, for each stimulus indicator in the sequence of stimulusindicators, a correlation between stimulus indicators in the windowcomprising the stimulus indicator and the predetermined number ofadjacent stimulus indicators, and reduced B-scans of the sequence ofreduced B-scans that are based on OCT image data generated while theretina was being stimulated in accordance with the stimulus indicatorsin the window; and the indication of the response of the retina to thelight stimulus generated by the response generator module comprises atwo-dimensional array of combined correlation values indicating theresponse of the retina to the light stimulus as a function of locationin the scanned region of the retina and time.
 10. The apparatusaccording to any one of claim 4, wherein the two-dimensional array ofcorrelation values comprises an array of one-dimensional arrays ofcorrelation values each indicating the response of the retina to thelight stimulus as a function of location in the scanned region of theretina, in which case the correlation calculator module is furtherconfigured to convert the two-dimensional array of correlation values toa sequence of correlation values by replacing each of theone-dimensional arrays of correlation values in the two-dimensionalarray with a single respective value that is an average of thecorrelation values in the one-dimensional array, the sequence ofcorrelation values indicating a response of the scanned region of theretina to the light stimulus as a function of time; or thetwo-dimensional array of correlation values comprises a sequence ofone-dimensional arrays each indicating the response of the retina to thelight stimulus as a function of location in the scanned region of theretina, in which case the correlation calculator module is furtherconfigured to generate a normalised two-dimensional array of correlationvalues by subtracting the first one-dimensional array in the sequence ofone-dimensional arrays from each remaining one-dimensional array in thesequence of one-dimensional arrays, the normalised two-dimensional arrayof correlation values indicating the response of the retina to the lightstimulus as a function of location in the scanned region of the retinaand time; or the two-dimensional array of correlation values comprisesan array of one-dimensional arrays each indicating the response of theretina to the light stimulus as a function of location in the scannedregion of the retina, in which case the correlation calculator module isfurther configured to generate a normalised two-dimensional array ofcorrelation values by calculating an array of averaged correlationvalues such that each averaged correlation value in the array ofaveraged correlation values is an average of the correlation values thatare correspondingly located in the one-dimensional arrays, andsubtracting the calculated array of averaged correlation values fromeach of the one-dimensional arrays in the array of one-dimensionalarrays, the normalised two-dimensional array of correlation valuesindicating the response of the retina to the light stimulus as afunction of location in the scanned region of the retina and time; orthe two-dimensional array of correlation values comprises an array ofone-dimensional arrays each indicating the response of the retina to thelight stimulus as a function of location in the scanned region of theretina, in which case the correlation calculator module is furtherconfigured to convert the two-dimensional array of correlation values toa sequence of correlation values by replacing each of theone-dimensional arrays of correlation values in the two-dimensionalarray with a single respective value that is an average of thecorrelation values in the one-dimensional array, the sequence ofcorrelation values indicating a response of the scanned region of theretina to the light stimulus as a function of time.
 11. The apparatusaccording to claim 2, wherein: the receiver module is configured toreceive a sequence of B-scans, which has been generated by the OCTimaging device repeatedly scanning the scanned region of the retina overthe time period, as the OCT image data; the apparatus further comprisesa B-scan processing module configured to segment each B-scan in thesequence of B-scans into a plurality of B-scan layers so that eachB-scan layer comprises respective sections of the A-scans forming theB-scan, and concatenate corresponding B-scan layers from the segmentedB-scans to generate sequences of concatenated B-scan layers; thecorrelation calculator module is configured to calculate, for each of atleast one sequence of concatenated B-scan layers of the sequences ofconcatenated B-scan layers, a respective rolling window correlationbetween concatenated B-scan layers in the sequence of concatenatedB-scan layers and stimulus indicators in the sequence of stimulusindicators by: calculating, for each stimulus indicator, a product ofthe stimulus indicator and a respective windowed portion of the sequenceof concatenated B-scan layers comprising a B-scan layer of the B-scanlayers which is based on a B-scan which has been generated by the OCTimaging device while the retina was being stimulated in accordance withthe stimulus indicator; and combining the calculated products togenerate an indication of a response of a layer of the retinacorresponding to the sequence of concatenated B-scan layers to the lightstimulus.
 12. The apparatus according to claim 11, wherein thecorrelation calculator module is configured to: calculate, as therolling window correlation for each of the at least one sequence ofconcatenated B-scan layers, a respective three-dimensional array ofcorrelation values, each three-dimensional array of correlation valuescomprising one-dimensional arrays of correlation values that have beencalculated using sections of A-scans that are identically located inrespective B-scans of the sequence of B-scans; and convert each of atleast one of the three-dimensional arrays of correlation values to arespective two-dimensional array of correlation values by replacing eachof the one-dimensional arrays of correlation values in thethree-dimensional array with a respective single value that is anaverage of the correlation values in the one-dimensional array, thetwo-dimensional array of correlation values indicating the response ofthe corresponding layer of the retina to the light stimulus as afunction of location along the scanned region of the retina and time.13. The apparatus according to claim 5, wherein: the receiver module isconfigured to receive a sequence of B-scans, which has been generated bythe OCT imaging device repeatedly scanning the scanned region of theretina over the time period, as the OCT image data; the apparatusfurther comprises a B-scan processing module configured o segment eachB-scan in the sequence of B-scans into a plurality of B-scan layers sothat each B-scan layer comprises respective sections of the A-scansforming the B-scan, and concatenate corresponding B-scan layers from thesegmented B-scans to generate sequences of concatenated B-scan layers;the correlation calculator module is configured to calculate, for eachof at least one sequence of concatenated B-scan layers of the sequencesof concatenated B-scan layers, a respective rolling window correlationbetween the sequence of concatenated B-scan layers and the sequence ofstimulus indicators by calculating, for each stimulus indicator in thesequence of stimulus indicators, a correlation between stimulusindicators in the window comprising the stimulus indicator and thepredetermined number of adjacent stimulus indicators, and B-scan layersof the B-scan layers that are based on B-scans which have been generatedby the OCT imaging device while the retina was being stimulated inaccordance with the stimulus indicators in the window; and the responsegenerator module is configured to generate the indication of theresponse of the retina to the light stimulus by generating, for each ofthe at least one sequence of concatenated B-scan layers, an indicationof a response of a layer of the retina corresponding to the sequence ofconcatenated B-scan layers to the light stimulus, by combining thecalculated correlations.
 14. The apparatus according to claim 13,wherein the correlation calculator module is configured to calculate, asthe rolling window correlation for each of the at least one sequence ofconcatenated B-scan layers, a respective three-dimensional array ofcombined correlation values, each three-dimensional array of combinedcorrelation values comprising one-dimensional arrays that have beencalculated using sections of A-scans that are identically located inrespective B-scans of the sequence of B-scans, and the responsegenerator module is configured to generate the indication of theresponse to the light stimulus of a respective layer of the retinacorresponding to each of the at least one sequence of concatenatedB-scan layers by: converting the three-dimensional array of combinedcorrelation values to a two-dimensional array of combined correlationvalues by replacing each of the one-dimensional arrays of combinedcorrelation values in the three-dimensional array with a respectivesingle value that is an average of the combined correlation values inthe one-dimensional array, the two-dimensional array of combinedcorrelation values indicating the response of the retina to the lightstimulus as a function of location along the scanned region of theretina and time.
 15. The apparatus according to claim 2, wherein: thereceiver module is configured to receive a sequence of B-scans, whichhas been generated by the OCT imaging device repeatedly scanning thescanned region of the retina over the time period, as the OCT imagedata; the apparatus further comprises a B-scan processing moduleconfigured to: segment each B-scan in the sequence of B-scans into aplurality of B-scan layers so that each B-scan layer comprisesrespective sections of the A-scans forming the B-scan, and concatenatingcorresponding B-scan layers from the segmented B-scans to generatesequences of concatenated B-scan layers; and convert each of at leastone sequence of concatenated B-scan layers of the sequences ofconcatenated B-scan layers into a respective sequence of concatenatedreduced B-scan layers, by replacing, for each B-scan layer in each ofthe at least one sequence of concatenated B-scan layers, the sections ofthe A-scans forming the B-scan layer with corresponding values of anaverage of A-scan elements in the sections of the A-scans; and thecorrelation calculator module is configured to calculate, for each ofthe at least one sequence of concatenated reduced B-scan layers, arespective rolling window correlation between reduced B-scan layers inthe sequence of concatenated reduced B-scan layers and stimulusindicators in the sequence of stimulus indicators by: calculating, foreach stimulus indicator, a product of the stimulus indicator and arespective windowed portion of the sequence of concatenated reducedB-scan layers comprising a reduced B-scan layer which is based on aB-scan that has been generated by the OCT imaging device while theretina was being stimulated in accordance with the stimulus indicator;and combining the calculated products to generate a two-dimensionalarray of correlation values indicating the response of a layer of theretina corresponding to the sequence of concatenated reduced B-scanlayers to the light stimulus as a function of location in the scannedregion of the retina and time.
 16. The apparatus according to claim 5,wherein: the receiver module is configured to receive a sequence ofB-scans, which has been generated by the OCT imaging device repeatedlyscanning the scanned region of the retina over the time period, as theOCT image data; the apparatus further comprises a B-scan processingmodule configured to: segment each B-scan in the sequence of B-scans(500) into a plurality of B-scan layers so that each B-scan layercomprises respective sections of the A-scans forming the B-scan, andconcatenate corresponding B-scan layers from the segmented B-scans togenerate sequences of concatenated B-scan layers; and convert each of atleast one sequence of concatenated B-scan layers of the sequences ofconcatenated B-scan layers into a respective sequence of concatenatedreduced B-scan layers, by replacing, for each B-scan layer in each ofthe at least one sequence of concatenated B-scan layers, the sections ofthe A-scans forming the B-scan layer with corresponding values of anaverage of A-scan elements in the sections of the A-scans; thecorrelation calculator module is configured to calculate, for each ofthe at least one sequence of concatenated reduced B-scan layers, arespective rolling window correlation between the sequence ofconcatenated reduced B-scan layers and the sequence of stimulusindicators by calculating, for each stimulus indicator in the sequenceof stimulus indicators, a correlation between stimulus indicators in thewindow comprising the stimulus indicator and the predetermined number ofadjacent stimulus indicators, and values of the averages calculatedusing B-scan layers comprised in B-scans that have been generated by theOCT imaging device while the retina was being stimulated in accordancewith the stimulus indicators in the window; and the response generatormodule is configured to generate the indication of the response of theretina to the light stimulus by generating, for each of the at least onesequence of concatenated reduced B-scan layers, an indication of aresponse of a layer of the retina corresponding to the sequence ofconcatenated reduced B-scan layers to the light stimulus, by combiningthe calculated correlations to generate a two-dimensional array ofcombined correlation values indicating the response of the layer of theretina to the light stimulus as a function of location in the scannedregion of the retina and time.
 17. The apparatus according to any one ofclaim 12, wherein: the correlation calculator module is furtherconfigured to convert each of at least one of two-dimensional arrays ofcorrelation values to a respective sequence of correlation values byreplacing each one-dimensional array of correlation values in thetwo-dimensional array, which one-dimensional array indicates theresponse of the layer of the retina corresponding to the two-dimensionalarray to the light stimulus as a function of location in the scannedregion of the retina, with a single value that is an average of thecorrelation values in the one-dimensional array, the sequence ofcorrelation values indicating a response of the layer of the retina inthe scanned region to the light stimulus as a function of time; or in acase where each two-dimensional array of correlation values comprises asequence of one-dimensional arrays, each of the one-dimensional arraysindicating the response of the respective layer of the retina (10) tothe light stimulus as a function of location in the scanned region ofthe retina, the correlation calculator module is further configured toprocess each two-dimensional array of correlation values to generate arespective normalised two-dimensional array of correlation values bysubtracting the first one-dimensional array in the sequence ofone-dimensional arrays from each remaining one-dimensional array in thesequence of one-dimensional arrays, the normalised two-dimensional arrayof correlation values indicating the response of the corresponding layerof the retina to the light stimulus as a function of location in thescanned region of the retina and time; or in a case where eachtwo-dimensional array of correlation values comprises an array ofone-dimensional arrays, each of the one-dimensional arrays indicatingthe response of the respective layer of the retina to the light stimulusas a function of location in the scanned region of the retina, thecorrelation calculator module is further configured to process eachtwo-dimensional array of correlation values to generate a respectivenormalised two-dimensional array of correlation values by calculating anarray of averaged correlation values such that each averaged correlationvalue in the array of averaged correlation values is an average of thecorrelation values that are correspondingly located in theone-dimensional arrays, and subtracting the calculated array of averagedcorrelation values from each of the one-dimensional arrays in the arrayof one-dimensional arrays, the normalised two-dimensional array ofcorrelation values indicating the response of the corresponding layer ofthe retina to the light stimulus as a function of location in thescanned region of the retina and time.
 18. An apparatus for processingfunctional OCT image data, which has been acquired by an OCT imagingdevice scanning a retina of a subject while the retina is beingrepeatedly stimulated by a light stimulus, to generate image datadefining an image that provides an indication of a response of theretina to the light stimulus, the apparatus comprising: a receivermodule configured to receive, as the functional OCT image data: OCTimage data that has been generated by the OCT imaging device repeatedlyscanning a scanned region of the retina over a time period; and stimulusdata defining a sequence of stimulus indicators each being indicative ofa stimulation of the retina by the light stimulus in a respective timeinterval of a sequence of time intervals that spans the time period; acorrelation calculator module configured to calculate a rolling windowcorrelation between a sequence of B-scans that is based on the OCT imagedata and stimulus indicators in the sequence of stimulus indicators; andan image data generator module configured to use the calculated rollingwindow correlation to generate image data defining an image whichindicates at least one of: the response of the scanned region of theretina to the light stimulus as a function of time; one or moreproperties of a curve defining the response of the scanned region R ofthe retina to the light stimulus as a function of time; and a spatialvariation, in the scanned region of the retina, of one or moreproperties of the curve defining the response of the scanned region ofthe retina to the light stimulus as a function of time, the spatialvariation being overlaid on an en-face representation of at least aportion the retina which includes the scanned region.
 19. The apparatusaccording to claim 18, wherein the correlation calculator module isconfigured to calculate the rolling window correlation between thesequence of B-scans and the stimulus indicators in the sequence ofstimulus indicators by one of: calculating, for each of a plurality ofwindowed portions of the sequence of B-scans, a respective product of astimulus indicator in accordance which the retina was stimulated whileOCT image data, on which at least one of the B-scans in the windowedportion of the sequence of B-scans is based, was being generated by theOCT imaging device, and at least a portion of each B-scan in thewindowed portion of the sequence of B-scans; or calculating, for eachstimuli indicator, a correlation between stimulus indicators in a windowcomprising the stimulus indicator and a predetermined number of adjacentstimulus indicators, and B-scans of the sequence of B-scans that arebased on a portion of the OCT image data generated while the retina wasbeing stimulated in accordance with the stimulus indicators in thewindow.
 20. A non-transitory computer-readable storage medium storingcomputer program instructions which, when executed by a computerprocessor, cause the computer processor to perform a method ofprocessing functional OCT image data, which has been acquired by an OCTimaging device scanning a retina of a subject while the retina is beingrepeatedly stimulated by a light stimulus, to generate an indication ofa response of the retina to the light stimulus, the method comprising:receiving, as the functional OCT image data: OCT image data that hasbeen generated by the OCT imaging device repeatedly scanning a scannedregion of the retina over a time period; and stimulus data defining asequence of stimulus indicators each being indicative of a stimulationof the retina by the light stimulus in a respective time interval of asequence of time intervals that spans the time period; and calculating arolling window correlation between a sequence of B-scans that is basedon the OCT image data and stimulus indicators in the sequence ofstimulus indicators.